We have no idea what Britt will call Nicholas. Some of his friends call him Nick and naturally suggested Uncle Nick, but Mother who hated nicknames (she always said if that's what she wanted us called that's what she would have named us), says he will be Uncle Nicholas when she says it. Daddy says if he has an Uncle Benji he can have an Uncle Nicky and Uncle Matty. Aunt Melanie suggested one of the names that Benjamin use to call him before he learned to pronounce Nicholas - Uncle Nonalas or Uncle Nickywas. As for Nicholas he said he can just call him his rich uncle. After all he doesn't really care because "Britt doesn't have a personality yet."
He tried to introduce Britt to Trixie (the cat), help him model his new glasses, tickle him, play with him, and he even managed to calm Britt down after he started fussing. I think he secretly likes his new nephew.