Is this unfair?

husband, myself and our 2 babies are visiting my Mum and Dad for a few days to catch up with the family and friends. We live 7 hours away. It was my eldest kids 2nd birthday so we had a imidaite family birthday party. We obviously supplied all the food for this and brought our supplies for our stay. While the party was on my Mum organised the family to come up again Sunday. My brother asked what he could bring for tea,aswell as my aunty. Mum told them nothing we have all we need. Later that day I poped to the shops to get formula for my daughter. I asked if my Mum would might watching the kids so my husband could come to and maybe we could grab a coffee for some alone time without kids. ( she offered when we first arrived to watch the kids if we had something we would like to do). She said oh that doesnt really suit me and made me feel guilty I even asked. She had nothing on mind you. So I rushed to the shops. She then went on and said while your there we need these supplies for tonight's dinner. I was a little annoyed we had to supply more food for everyone when my brother literally asked if he could bring anything and she said no. Once I got home my sister rang and said oh I cant be bothered coming anymore but sent her daughter Sara with my brother up for tea and then to stay the night. She didnt bring anything with her. Then my Mum said to me oh you should take your kids to the beach tommorrow and drop Sara off home. It's a 45min drive. I'm not sure why I'm so annoyed I just feel like they think were rich or something. We have been living off 1 not so good wage for 2 years with 2 babyies. Plus we had all these expenses just to visit. I'm not sure how to tell my mum I cant really afford it. She then gets annoyed we dont visit more often. It cost us a small fortune everytime we visit. My husband is so annoyed he wants to go home. I feel so stressed tryin to keep the peace.