I'm sorry for the hell you are going through, been through it myself with my jw convert.
My kids at the time were not as young as yours but I never, ever allowed them to step foot in a kh! ever! He naturally wanted to bring them but then I said fine, every other weekend they are going to explore the religions of the world including Catholic (you know how much jw's hate Catholics especially), Lutheran, Baptist, Hindu, Buddist, etc..etc... That stopped his attempting to bring them to a kh. What happened next? he would attempt to preach at them or make them read jw litter-ature. I then suggested they would be reading my apostate literature to get a balanced view of things. That worked somewhat, he would attempt to preach at them when I wasn't around. I then decided he should not be alone with the kids as much as possible and if they went somewhere I went too, family time you know. Was this difficult to do? yes, very and it was a hellish time in general.
Kids are smarter than people give them credit for in my opinion. Kids can and do figure out that jw's are nutty than fruitcakes if given an alternative view of the world and religion. Bring them to a library and read some children's books about Bible stories and Jesus and see how that changes their views.
What worked best in my home was to make sure it was a neutral zone of sorts. Absolutely no wt or jw literature could be lying about anywhere, nor could it be read in public view. Well, my jw could have but then I would find my apostate literature and keep that out or find the most horrible story about jw's I could find, print it out and read it in public view. There is no lack of horrible stories involving jw's.
Is this an optimal way to live? no. However, if you can manage to go through a bit of hell to protect your kids minds, souls and body from the dangers of this cult and its members then it will be worth it. My kids have since grown up and found their way in life and have gone on to become Christians. They love their dad but think he is just nuts in the religion department. Yes, they know all about cults but in the end 'he is nuts' is the general consensus. Sometimes knowing jw literature is your best defense. Most jw's do not know or remember their own doctrines so when necessary you can pull out 'your own literature says....' It disgusts me no end to have to study jw doctrine but 'know thy enemy' is not a bad way to go at times.
I was literally panic stricken when this all first happened in my home. Lost so much weight my poor dad thought I had a terminal illness. I too, lost all zeal for life and was obsessed with keeping my kids safe and trying to find a way to get my jw out of the org. I studied and studied more about cults, jw doctrine, Bible study, you name it I tried it. In the end we cannot make our spouses see the light when they are kept so busy in the cult they don't have time to come up for air much less ponder the reality of what they are taught day after day by the wt. You can help your children though. Not only can you have some control over what they learn you must. As a parent it is your duty to keep them safe and this includes their minds. Teach them to think and to think for themselves. God gave them a brain, did He insist they not use it?
Things can get better.
In talking with many ubm's (unbelieving mates) over the years they all have their own way of dealing with this situation. Some stay in the relationship just so they do have more control over the situation. It is much easier to see what's going on when you actually live in the same house. One ubm I know was intent on staying until the kids turned 18 just because he felt it was his duty as a man to be there for them, then his plan at the time was to roll out of there on his cycle once the last one turned 18. Others will go to the occasional meeting to keep some peace but still do holidays and try and keep things as normal as possible in the home. The men seem to have an easier time in my opinion because they can pull out the 'head of the house' card when necessary.
If possible put a stop to all the meetings, if not, then make an agreement that only every other weekend will they go and every other weekend you get the kids. Then plan lots of fun activities! make the days with you so enticing the kids will dread the kh days! Plan fun weekends and always ask the wife to go with, leave it to her to choose between family or cult. The kids will eventually see the wt for what it is.
Lastly, if you cannot stay in the relationship start getting all your ducks in a row now. Don't forget to get your own power of attorney regarding the blood issue for yourself and by all means let your kids schools, doctors and non jw family & friends know you will allow blood for yourself and your kids. Make sure the doctor writes it down in the kids records. Do not rush into a separation, it is your home too.
Start a record of harmful things the kids have said to you (about satan, the big A, etc.) record things so you have them if needed. Somebody suggested Rick Ross, he is a legitimate service to use or could be helpful for you. So is Witness Inc (google it) if memory servese me Duane Magnini (sp?) runs it and has info on lawyers that know about jw's. An attorney off the street will not understand all that is involved with jw's and the psychological harm that it can cause children nor will the typical psychiatrist unless they are schooled in cults.
Some courts do not understand that jw's are a dangerous cult and see any religion as a 'good' thing for kids. You may have to consider joining a church yourself and bring the kids so if it comes to it the judge will look at which 'church' is best for the kids and naturally a church with youth programs and fun things will be choosen over a kh. Just a thought.
Things can get better, really. We have finally found a truce of sorts in life though that huge elephant is always sitting in the room. Find ways to find her authentic self and weekend getaways or even Sunday fun outings can make life more tolerable. Anytime you can get them to miss meetings is a good thing. As akward as it may seem now, try to find couple time together to find your way back to each other.
Wishing you peace,
carla