I am sure you can find positive things for your situation.
Perhaps you wont be able to play online Wii U to Wii U with your cousin, but if your cousin wants to play games with you, can always come over to you or you can go to your cousin.
And if you hang out alot, then PS4 + Wii U = more games for you two to play.
When your at your cousin house = Wii U exclusive games
When at your house = PS4 exclusive games
So there is a positive side to it.
Anyway if you dont hang out alot, then i suggest getting the console that you prefer.