I have a question regarding feeding a non-muslim. Is it permissible to feed a non-muslim a food that is not zabiha halal. For example, if I were to buy a food that I find out to contain gelatin, is it permissible to give this to a non-muslim? Or would it be permissible to buy a non-muslim a non-zabiha chicken burger?

It is permissible as long as it is not pork alcohol. So yes you can give them non-halal marshmallows or chicken.