My family is like this too hahahaha, of course its on a smaller scale and they will do it in moderation. I absolutely understand how u feel when seeing your parents or other family members insisting to pay for their fair share of the food etc. Often I would see my aunts or grandfather trying to pass back the money to my dad whenever he bought anything for them. It was quite a struggle for him hahaha but that scene was quite heartwarming.

What my point is that the key word should always be moderation. Sometimes it's okay to let them pay for the food or any other things depending on the situation. But if they are doing it on a frequent basis or even wanting to pay the ingredients when your wife baked for them, then perhaps you can try this:

Mom and Dad, do you remember the times when my other siblings and I were young, and we did not have the financial means to pay u back? You did not demand any payment from us and instead raised us to become fine adults. You raise us wholeheartedly and told us that we should be fair in everything that we do. Now I'm married too and have left your care and guidance, just like how the baby birds can finally fly and feed themselves. Hence, that's the reason why my wife and I would like give back to u guys for all those years of love and support. I don't believe that financial compensation in hard cold cash is truly meaningful. That is why we did all those small gestures like baking cakes/pastries etc and taking u guys out for a meal.

To my siblings, when we are doing gift exchange, it's okay to get a gift that's a lower or higher monetary value than my gift. You do not have to pay back the difference in amount just to make it fair. It's the thought that counts when giving a gift to someone else.

For both scenarios above, you really do not have to pay as it will diminish the value of all the sincerity from each family member. If we really count every cents and pennies, all of us will feel drained and all these meaningful family tradition will become a family transaction. We are a family, and monetary issues of who's paying should never be the highlight of every family meal. I just wish that we can all try to make a small step forward by spending more time with our family, and not spending money to even out the monetary differences :)

This is just an example hahahaha, do adjust it accordingly. All the best to you!