How to make time for yourself

Feeling really selfish right now but I’m struggling..
I am married to a well meaning husband, I do adore him but as far as help goes he will help a little, he works long hours also, but as far as emotional support it’s not really his area. we have two young kids that are the usual demanding and messy as kids are. I’m forever chasing my tail keeping on top of the basics as I work part time too. I already have little time for myself for eg gym and downtime. To add to this I have a demanding mother, she’s very opinionated and is forever telling me what I need to do for parenting, projects around the house, suggesting my husband does more and what she suggests is usually something not on my to do list, and expects me to provide her emotional support. Grumbles often I don’t do enough with her like lunches or shopping dates. When I do get a day to myself with no kids home and I might get some house chores caught up she will drop in and stay for hours til school pickup talking about what she saw on Facebook.. I often suggest activity’s for her to do, even walk to the local cafe for a coffee! But she refuses, rather be on Facebook and not create herself fun things to amuse herself. I get she’s bored and I enjoy our time together I was ever hopeful she’d want to find some things to enjoy independently from me.. but she’s just been diagnosed with cancer, and I know I’ll have to be taking her to appointments and have to help her more than ever but I’m concerned that her expectation of me helping her will take away from my home life and my husband really won’t understand. So I am feeling pressure from every direction trying to keep everyone happy. So my question is anyone got any tips on how to juggle it all, of course I want to help my mum but I also have young kids and a husband who need me too, so I’m feeling stressed about it all right now : (