Family Dinner Etiquette or Just Rude?

Question on family dinner etiquette.
In my family, if you invited another family member over for dinner you hosted the meal and possibly dessert if they didn’t offer to bring one. But you never expected them to pay since they are family and you were the one to extend the invite.
My husbands family is not this way. When my brother in law and his wife invite us over for dinner; they ask us over, wait for us to agree, and then say great, will you grab half the food or just pay us half the cost of the food in cash.
Is this normal for other families?
Like the first time they invited us over, they asked 2 weeks in advance but only asked for cash two days prior to the dinner.
Also, while half seems fair at the surface level they have 5 kids. It’s just my husband and I eating since our child is too small for solid foods yet. So a family of 7 and a family of “2” eating but splitting the cost down the middle. Mind you, when we ask them over we don’t ask to split it and they never offer to help one way or another.

What are your thoughts? Is this considered rude or am I just clashing because I was raised differently.

I don’t like that they make you pay half when they have more in their immediate family. It’s just you guys so how is it fair that you’re paying for yourself plus some of them. In my family if you get invited to dinner that normally means they’ll pay for it, or maybe it’s just because I’m the youngest in the family. If your husband doesn’t have an issue with it it may just be how they do things in their family