You are so lucky to have an ex that is supportive of homeschooling. Hold tight to that thought. I have seen so many threads where mom wants to homeschool, dad wants school. In a local case judge supported dad and ordered school for older child and teen, both had always homeschooled and wanted to continue to homeschool. The next day dad got on a plane and left mom and boys to deal with this unhappy development.
My husband's ex-wife was atrocious on so many levels. The most important thing you can do is find a way to get along. Maybe look for alternatives to meet his need to give the kids a socially expected education while keeping it unschooly.
For example, we buy the secular books listed at www.sonlight.com
. Our kids love the books and it is exposing them to topics I wouldn't considering exposing them to. We essentially strew the books or sometimes I'll just say, "I'm reading this book now." The books are so good and the kids learn a lot.
We also have the living is learning guides. http://www.fun-books.com/books/livin...ing_guides.htm
I have them to see if my kids are learning the socially expected things or not. I look at them and decide if that skill is something I want my kids to have. If so, I introduce it in a laid back way. My kids are still little, but I'm thinking of first grade math--kids will be able to count by 2 and 5. We already do that in games even though he's still 4. He's not competent at it but he is introduced to it and it's fun.
The more you support your ex's desires now the more likely he is to remain pro-homeschooling. Don't get stuck in the "your way or the highway game." I don't think his goals are that difficult to meet in an unschooling format. Frankly, I'm trying to do the same thing in my own way. So just be creative and you will find a solution. The alternative is he could always go to a judge and ask the judge to order school. Get along with your ex for the sake of the kids.