all the translations of valonqar that are given say cousin
In truth, cousin is true of the king's brother to.
Well, that is also correct.
The words for "brother"/"sister" also refer to cousins of tye same gender in HV, so valonqar for a younger male cousin is correct.
Parallel cousins only. The words for cross-cousins are different. Here's a helpful little chart which everyone's favourite Dedalvs made: https://bit.ly/2H726Mw