Yes, separating the issues into more manageable ones, could help. Especially separating everything you can from your relationship with MIL.
Below is just one possible way of looking at the issues, as I see them. You don't have to agree. But it might help.
First, there's the issue of your poor relationship with MIL. You are under no obligation to maintain ties with her yourself. While it would be nice for your son to maintain ties with his father's family and heritage, it can be on your terms, not hers. What about FIL? Uncles? Aunts? Cousins? They can all be people who, if any are not toxic, could help maintain those ties while minimizing any contact you may have with MIL.
Then, there's the issue of your conversion. Which seems to have been under duress and not from the heart. You don't have to remain Jewish yourself. At the same time, you don't have to look on it as a bad thing you did under duress (even if that is how you feel about it now). You could chose to see it as a gift you gave to your husband because that was the only thing that would allow his son to be born Jewish. A gift to your husband, your soulmate. Not something you did for MIL. Because, in many ways it was a gift to him. Find peace in that gift. Even if you don't remain Jewish yourself.
Then there is the issue of your son's religious education. As many have said, you son is currently Jewish. But you *can* certainly raise him as a Jew and not be Jewish yourself and simultaneously expose him to your beliefs (should you go back to a Christian denomination). Teach him both. Simultaneously. Let him take part in those elements of the Jewish faith (Passover seder, high holidays, bar mitzva, etc.) that will give him the ability to live his life according to whatever beliefs he choses as an adult. But it doesn't have to be done with MIL. You can find a different synagog for him.
One thing my (Jewish) stepdad said at last year's sedar was that as parents, Jews do not have the obligation to ensure that their children become practicing Jews. Their obligation is to provide their kids with the knowledge they would need to do so if they so choose as an adult. An "obligation of means" rather than an "obligation of results", if you will.
On Hebrew school, my brother and sisters went... after school classes once a week or so for a few years. That's all. Ultimately, no matter what religion they may adopt in their adult lives, even if they convert, learning a second (or third) language is never a bad thing.
And none of any of it forbids you from also teaching him about what you believe simultaneously.
You can choose to see a "Jewish education" as a gift you give your son--the gift of additional ties to his father's heritage, and thus to his father himself.
You can choose to approach this "Jewish education" as giving your son knowledge of his father's heritage, rather than as an attempt or obligation to ensure that your son *believes*.
I'm not Jewish (my mother converted after I was born). Went to Catholic schools. Lived in a Jewish home. Celebrated Christmas and Hanukah and Easter and Passover. It wasn't confusing for any of us. And it made my life richer in many ways.
I hope you find a path to peace that works for you and your son. That works with and for the memory of your husband. Whatever that path may be.
As for your MIL, it's up to you and a separate issue. Whatever you decide about her, don't let that dictate your other decisions. Your terms. Not hers.
Edited by Ione - 4/8/11 at 12:15pm