Well.
We know many couples get married in church without having Christian faith. People even get their babies Christened because it is the cultural tradition rather than them being active Christians.
When marrying, respect for partner’s family’s faith is important and there will be many cultural traditions that a partner will want to continue. Whether it be boxes of mithai and fireworks at Diwali , Christmas Tree, Seder, or whatever.
But OP, I think you need to talk seriously about all the ways that he himself feels pressured and obligated, and how far this will affect you. And how far it will amplify if / when you have children. They may well expect to visit for months at a time. With expectations of having significant influence on your daily life.
Your DP needs to know that it would be as hard for you to live with that as for him to be more honest with his parents.
What household cultural things will you be happy with? E.g Pork-free, no problem. Accept an invitation to Iftar, the children have Eid presents, etc, fine, part of the respect and cultural enrichment. What will he be happy with? Christmas tree? Kids in school nativity / carol service?
There is the circumcision issue… what does he feel about that? What if his parents expect to see a young teen daughter wear hijab outside the home? (Would they?).
They will visit, they are his family. Yours too. You will probably visit: it’s important (IMO /IME) for children to understand and appreciate the full breadth of their heritage.
Amongst my family extended as far as cousins we have Jewish/Christian, English/Japanese, English / S.Asian, English / Kenyan, Christian / Hindu combinations, all of which have nearly broken people at some stage, but all eventually negotiated. But that is because all the individuals involved were able to put respect and understanding above absolutism or a power struggle.
Talk, talk and talk some more about where exactly his own boundaries fall, and yours.