Hi, I think JGNAT had good advice(she has picked up a LOT as a non-JW, I am impressed).
I think going to some meetings with your mom before the wedding and softening her up could be a good thing. If you are in a different cong. all the better for you-even if you just show up now and again after the wedding(and face the consequences, if they care to inflict them upon you), no one can give your mom grief and she won't feel bad communicating with you when the grandchildren come around, and your sisters won't be nasty to your wife(to- be) since they will want to finagle her into the organization. It would be a nice gift to give to your mom who seems so firmly entrenched. She needs a good son to be able to lean on unconditionally, and we know that everyone else she is involved with is pretty much 'conditional'. Just let her know that there are no circumstances which would ever cause you to reject or ignore her(if this is after a sis's emotional/religious blackmail, so much the better).
Good LUCK, God bless, and hug your mama! Shelly