My advice to you is as follows:
I would NOT DISCUSS ANYTHING with the "elders"; except to greet them as you would anyone else your wife would be friendly with. Do not give them an inch in your household or marriage, Do not allow the elders of the Watchtower to dictate to you how you should be running your marriage or your household. Simply said; do not let them in or even acknowledge them.
As for your children; you are still their father and that is the final word on their welfare; not the elders or the teachings of the Watchtower. Your wife is their mother and I am sure loves them as you do; but you must be firm about any teachings which would affect their future.
As for your wife; the hard fact is that she will never leave you ( unless she is independtly wealthy and does not need your income) because you pay the mortgage ( or rent) and support her and her children. That economic base gives you leverage in the future of the household. If she threatens to leave you I would say "go ahead, there is the door" but would let her know that she; as the "abandoning partner" would have a hard time getting custody of your children in a court of law.
I say rise above the banter of JW mixed marriages. Allow yourself to be tolerant of your wifes involvement; to an extent. Certainly do not fear the elders or their threats or promises. Do not validate their beliefs by allowing yourself to meet with them. Shut them down before it gets to that point. Dont forget; this is YOUR household and YOUR children. You are their mentor and legal guardian. Do not allow anyone to convince you otherwise.
Let her go to meetings and worship as she pleases.After all, this is America and we pride ourselves on freedom of worship. However; on no UNCERTAIN terms would I allow the JW thinking to infiltrate your thinking or the future of your children ; as in sacrificing their college education or their future for preaching work or "going to meetings".
Allow her to discuss the JW beliefs at family dinners and you can listen and offer a counter belief. This will show your children that differences can be discussed intelligently and your counter lifestyle to your wifes JW one will show the children that there is another way to live your life reasonably. This works in my home; although my wife is catholic.
If your wife tries to force the children in field service or to meetings of which they do not want to participate; I would intervene in their defense. Most children do not want to be Jehovahs Witnesses. I know this for a fact as I was raised as one. The effects were devastating.
.good luck, frank