Too many eggs in one basket.

[Angel Eyes]

Why did Rhaenyra have two of her elder sons betrothed to their Velaryon cousins? Would have made more sense to have one betrothed to a Velaryon daughter and have another to betroth to another great house, i.e. House Baratheon, where Borros Baratheon had four daughters.

[Lord Varys]

29 minutes ago, Angel Eyes said:

Why did Rhaenyra have two of her elder sons betrothed to their Velaryon cousins? Would have made more sense to have one betrothed to a Velaryon daughter and have another to betroth to another great house, i.e. House Baratheon, where Borros Baratheon had four daughters.

The impression we get is that the Baratheon girls are somewhat older. I mean, Boremund Baratheon was born around 50 AC, or so, and he died just quite recently. That makes it likely Borros himself was born in the 70s AC, making daughters closer to Rhaenyra (and her older half-brothers) in age than to Rhaenyra's sons.

Rhaenyra made those betrothals when both her sons and Laena's daughters were still very young. A marriage pact with a Baratheon daughter would have been an awkward affair - Jace or Luke would have likely have married a woman in her thirties when they were mid-teens...

[Angel Eyes]

But what about anywhere else? Were there no other eligible young women?

[Lord Varys]

1 hour ago, Angel Eyes said:

But what about anywhere else? Were there no other eligible young women?

How should I know?

The idea probably was to ensure that a biological descendant of Corlys and Rhaenys does not only sit the Iron Throne (in Baela's child by Jacaerys Velaryon) but also inherits Driftmark eventually (in Rhaena's child by Lucerys Velaryon).

Besides, Laena Velaryon was the rider of Vhagar when those betrothals were made. Rhaenyra needed her and Daemon both when the time came to take her throne. They were both more important than the support any great house could muster.

[Megorova]

I think that Rhaenyra's three sons weren't children of her Velaryon husband. He was gay, and that children's father was one of knights in Targaryen court (don't remember his name, but those three boys looked like him). If that is so, then three of  Rhaenyra's sons were only half dragonseeds.

Thus if they have married with someone, that were not a dragonseed, then their children would have been only 25% Valyrians/dragonlords, thru their grandmother Rhaenyra. Maybe that amount of dragonblood, would have been not enough for them to become dragonriders. So to compensate impurity of her children's blood, Rhaenyra had to marry them only with other dragonseeds, such as members of Velaryon family.

First Baratheon was half-Targaryen, then his descendants intermarried once with Velaryons, and once with Targaryens (that's prior Robert's grandmother Rhaelle). Furthermore, dragonlord blood of Targaryens, from that single marriage between them and Baratheons, remained in Targaryen family.

(Jocelyn Baratheon + Aemon Targaryen = Rhaenys Targaryen + Corlys Velaryon = Laenor Velaryon, Rhaenyra's husband, who (probably) was not father of her three sons.)

So probably that amount of dragonblood, was not enough, for any of them to become dragonriders. Four daughters of Borros Baratheon had 12,5% of dragonblood from their great grandmother Alyssa Velaryon, and 1,5625% of Targaryen blood from their great great great grandfather Orys Baratheon. 14% of dragonblood in total.

Though if Rhaenyra's sons married with Velaryon girls, children born from those unions, would have had 75% of dragonblood. Thus what you called "too many eggs in one basket", probably was done for the sake of purifying blood of Rhaenyra's descendants. Rhaenyra's two younger sons Aegon II and Viserys II had 100% pure dragonblood. Thus to keep their dragonlord blood pure, they were supposed to marry with other pureblooded Valyrians.

[The Bard of Banefort]

This site is generally pretty pro-Rhaenyra, and while I certainly prefer her to Aegon, she does have some less-than-noble qualities. She arranged those betrothals because she didn't think out how it could negatively impact their futures. Rhaenyra was proud and short-sighted, so she betrothed her sons to the closest thing there was to the Valyrian royalty of her family--the Velaryons--without considering that she would need more than the Velaryons' support to claim the Iron Throne. 

As others have mentioned, it would also add legitimacy to her clearly illegitimate children, who were another product of Rhaenyra's short-sightedness and vanity. 

[Deepbollywood Motte]

6 hours ago, The Bard of Banefort said:

This site is generally pretty pro-Rhaenyra, and while I certainly prefer her to Aegon, she does have some less-than-noble qualities. She arranged those betrothals because she didn't think out how it could negatively impact their futures. Rhaenyra was proud and short-sighted, so she betrothed her sons to the closest thing there was to the Valyrian royalty of her family--the Velaryons--without considering that she would need more than the Velaryons' support to claim the Iron Throne. 

As others have mentioned, it would also add legitimacy to her clearly illegitimate children, who were another product of Rhaenyra's short-sightedness and vanity. 

I always got the idea that Martin wrote the Dance kind of pro-blacks. I have to say that I didn't read the side-stories, just the wiki and forum on the Dance so maybe I got that idea because fans are generally pro-Rhaenyra (the fact that the fan-favorite North was on that side does help off course).

Adding legitimacy to her childeren seems the most logical to me and why give your line "inferior" blood if holy pure Valyrian blood is an option (that seems the line of thought of many Targaryens).

[The hairy bear]

On 17/2/2018 at 9:27 PM, Angel Eyes said:

But what about anywhere else? Were there no other eligible young women?

Your analysis would be spot on in later generations. But the key issue here is that both Baela and Rhaena had been given dragon eggs at birth, and were potential dragon riders. An additional dragon-rider was much more valuable than an alliance with another family, even if they were great lords.

More importantly, marrying both the Velaryon families into the Targaryen family ensured that they did not marry to another family. Any great house they married into could have become another family of dragonriders. The Targaryens should do their best to prevent this.

In fact, this is what happened with the Velaryons: the marriage of Rhaenys to Corlys had made the Velaryons a dragonriders. In order to avoid them to become a rival family, Viserys and Rhaenyra were wise to promote marriages between the two houses to keep both lines united.

7 hours ago, Deepbollywood Motte said:

I always got the idea that Martin wrote the Dance kind of pro-blacks.

While it is true that Rhaenyra is more sympathetic than Aegon II, and the greens are the ones who attacked first (killing Beesbury and Lucaerys), it can't be said that the blacks are depicted favorably. Specially the two black leaders (Rhaenyra and Daemon) are shown as petulant, fickle, cruel and unfit to rule. Meanwhile, many green characters are shown in a good light: Daeron the Darling, Helaena,...

[Angel Eyes]

On 2/19/2018 at 11:32 PM, The Bard of Banefort said:

This site is generally pretty pro-Rhaenyra, and while I certainly prefer her to Aegon, she does have some less-than-noble qualities. She arranged those betrothals because she didn't think out how it could negatively impact their futures. Rhaenyra was proud and short-sighted, so she betrothed her sons to the closest thing there was to the Valyrian royalty of her family--the Velaryons--without considering that she would need more than the Velaryons' support to claim the Iron Throne. 

As others have mentioned, it would also add legitimacy to her clearly illegitimate children, who were another product of Rhaenyra's short-sightedness and vanity. 

I guess the Arryn ancestry was never brought up in their appearance.