Ring bearer

We skipped flower girl/ring bearer entirely.

It's not remotely required - MOST things people tell you that you "have to have" are not required.

ACTUALLY required:

1. A couple

2. A license/officiant (some places you don't need an officiant)

3. Food for any guests you may have

That's it.

Sum total.

It's not a requirement, so you can do it without him although I'm sure you probably don't want to. Hopefully by your wedding date your sister and you can come up with some sort of agreement because I know me personally I would HATE if my sister pulled my niece/nephew out of my wedding

My fiance and I are not having a ring bearer or a flower girl in our wedding. We decided to go a different route when it comes to those positions.
My son, from a previous marriage, is a junior groomsman but will be in charge of the rings since he will be apart of our ceremony and with one of the groomsman once he reaches halfway down the aisle he will stop, spin a fanny pack around to the front of his waist, put on sunglasses, start tossing flower petals out from the fanny pack and dancing down the rest of the way.

Like others have said, you don't have to have a ring bearer. But, if you want one, have you considered any girls for the job? The ring bearer doesn't have to be a boy. Heck, some people use a dog.