This is a HUGE burdeon for anyone to undertake--let alone someone who's only 25. You can't force your sister to go to rehab and you can't make her stop drinking. Hopefully, she'll do that one day on her own.
My advice to you (since you've asked for it) is to spend a lot of time on this forum reading as many posts as you can, so you'll be fully aware of the extent of the drama and problems you're considering inviting into your home, into your life, into your wife's life, and into your future children's life.
It's also a good idea to thoroughly research alcoholism and addictions in general so you'll understand how incideous a disease it is and how it affects everyone in the family.
I'd also suggest that you attend at least 6 Alanon meetings in your area. There you will meet family members of alcoholics and addicts and you'll see first-hand how much damage living with an active addict does to the people who love them.
You're about to invite chaos into your home. You're about to invite an active alcoholic into your home as well as a child who's violent and has anger-management issues.
You're willing to give up your serenity. You're willing to give up your wife's serenity. You're willing to take on the financial burdeon of an active alcoholic and three children. You're even willing to put your plans to have children on hold.
This is a recipe for disaster. The best way to help your sister is to let her learn how to take care of herself. Don't invite her into your home. Don't send her money. Send her a listing of AA meetings in your area.
Don't take in a child who's displayed violence into your home. Call social services and have them check on the children.
I'd think seriously before I make any of the moves that you're considering. And I have to ask why you're thinking of throwing away your life, your wife's life, and holding off on having children to save someone who doesn't want to be saved.
Please educate yourself before you take on a burdeon that's too much for you and your wife to bear.