I need help and this situation is keeping me up at night.

M • ❣️
I am only 4 weeks pregnant ☺️ and I told my inlaws today, they were so excited. My other halfs family is full tongan and my family is New Zealand. Both polenesians but two very different cultures. 
As soon as I told them, they said they were going to name my baby after a passed relative. They also said we have to marry with only the parents attending  and that I have to start attending their church. I am Mormon not catholic. They said they're going to look after it while I'm working which I am grateful for. But I'm not sure. This is the first grandchild on both sides and I can already see our families dividing. I want to keep both grandparents happy but I will say what I need too because this is our first born. 
Can someone help me, it's really stressing me out ?