Welcome to the forum.
My wife and I are also now "inactive" 3rd generation JWs with big JW families going back to Russel and Rutherford.
Please use an answering machine to keep a legal record of messages, and keep a diary of events. Keep mum on your JW opinions for now, and remain simply "inactive"...the less said the better for right now.
By all means, see a family law attorney. and follow their instructions to the letter. With 2 sets of JW grandparents and a future EX with financial backing, custody may become an issue. You may need to navigate JW "law" and the courts adroitly...usually the less said the better....for now. Depending on where you live, a legal separation may be a good financial (and JW) option to obtain legal protection, alimony, and child support while awaiting the necessary "wait" time for a divorce. If your ex is having an affair he may become more open about it.
Hang in.