Spin off to uneven BPs

What excatly is the role of an usher? How is it different from a Groom's man?

I have a MOH
3 BMs

FH has

1 BM
4 Gm

2 ushers

it's 7:4

I was going to invite 3 of my cousin's but 2 of them are also 08 , one 6 months before me, one 3 months after me. The other lives on the other side of the country & just had a baby. I am now afraid that by asking them I will be puting them in an awarkward finical position, or worse my cousins may invite me to be in their BP just b/c I invited them

what would you reccommed for this? We are having a small wedding about 120 expected guest......


TIA

you girls always know how to handel these things properly