The entries of Aegon III and Viserys II both name Visenya explicitly as their "only sister" ("This pregnancy led to the birth of Viserys' only sister, named Visenya." "This pregnancy led to the birth of the only sister Aegon would have, named Visenya"), but Baela and Rhaena could probably count as sisters as well. They are however not mentioned unlike the three Velaryons. Visenya could be the "only full-blood-sister" or "his mother's only daughter".
House Strong is still said to hold Harrenhal between 1 AC and 196 AC. I think the date can be narrowed down to "between (several years) after 48 AC (death of Haroways) and (before) 151 (Lucas Lohstone receives Harrenhal) or 131" (mentioned as year, the house died out, though that would mean that Harrenhal stood empty for 20 years). Stafford Lannisters page contains the sentence "His wife is not mentioned" right above the family tree, though myrander is listed there.