Is it too hard to say please and thank you?

I help out a family that needs a lot of help and I know them socially, so we are trying to maintain an equal kind of relationship even though I am better off financially. I just like for our kids to hang out and not have huge expectations about spending money but I feel like when they are over they expect that I will buy anything or do anything and take it personally if I don't. I try to explain to the mom that i am feeling the pinch lately but she just looks at me like yeah right. she has no idea how much my mortgage is or anything and it makes me mad. she is a nice person and works really hard but I don't feel she respects me and it comes down to how her kids treat me. I don't want to dump her as a friend, but i feel kind of used and kind of like she compares me to another friend that does a lot for her and spends a lot of money on her. she's been there for me at times. so I don't know what to do