Small feeding Issue

I have a ball python that is I'm currently feeding large mice, he/she is 247 grams, I think he needs to move up to rats but the problem is that my mother is a rat lover so she won't let me do that.

Could I just feed him 2 large mice or any other combinations?

Yes, you can. One reason why people switch to rats is to avoid feeding multiple mice as their BPs grow, but if that's your only option, then by all means go ahead.

She needs to get over it. That is just part of having a snake. Feeding several mice is going to get annoying when your snake gets full grown.