PALE EMPEROR- Hey man- I'm really sorry that you're having to deal with this situation. It really sucks big time. It does sound like your mom and sisters are going to support your decision at least as far as not shunning you. And that is a good thing. My older mom is like that also. I left the organization 13 years ago- and she's never shunned me- always supported my decision.
As far as dealing with your wife's relatives - that is where the big challenge is going to appear - it seems. One of the biggest challenges you will probably face is not having your brother in laws wife badmouthing you to your young daughter. This WT organization and JW cult indoctrinates these people to be the worst gossips on the planet. AS you've already discovered with your brother in laws wife- many JW's do NOT honor personal boundaries - not even when it comes to turning our young children against us in a personal way. I know. After I left 13 years ago- my fanatic JW ex-wife did EVERYTHING in her power to malign my reputation to my then teenage daughters and my son. My son didn't buy into the crap- but my girls did. It's been hell trying to rekindle a relationship since.
No easy solutions here. But because your young daughter STILL lives with you- you have that to your advantage. Take the opportunity to make sure NOBODY in your wife's family is feeding your daughter JW BS into her little head about you, INCLUDING your wife. Take the time to spend time with your daughter to do fun things, show her you love her, take her on walks, etc. - because mommy's JW family will probably try to influence your daughter's mind. ALSO- Another biggie in my opinion is this - make sure that you and your wife are on the same page concerning HOW MUCH she will/or will not discuss your religious differences with others or your daughter. Tell her that you do NOT want her using these differences as a dividing tool in order to rob your home of peace. A a JW female- your wife is still a " JW wife " and should at least show you respect as the " head of the house " - at least in JW terms and definitions in a physical or providing way. And emotional way too. Your wife might try assuming the so-called " spiritual headship " on her own- but do NOT let her disrespect you in other ways. You deserve more than that.
Please know that we are here as a support to you my friend. If you ever want to chat just PM me and I'll give you my number. Hang in there. we've got your back