Family wedding issue?

ok, here's my beef, my brother is getting married, and we're from a reasonably close family. my other brother (its just the 2 boys and me..) is best man, and the other groomsman is a friend. my brothers fiancee doesnt have any friends (its sad i know) we get along well but dont see each other much outside of family things (so a few times a week.) she asked my cousins who live interstate (11 +13) who she's met once (in the 8 years shes dated my brother) to be her bridesmaids. this irritated me a little because i couldnt understand why someone she's met once got picked before someone she's known 8 years. but i got over it (i convinced myself i would outshine her if i was in the wedding party...its sad, but it helped me get over it) but now they want me to sit up the back with their daughter (nearly 1) at the ceremony, so i can take her outside if she starts to fuss. do i confront them and tell them i feel a bit used but unwanted, that i dont even sit with my family? or just deal with it