I understand your reply (second half below) but your original post was really worried about money - and why you needed to change (first half below). So I am going to give you a very gentle "face punch".
You have choices, right now you are choosing to let your mother spend her money on whatever she wants while you carry most of her costs - same for your niece, in a smaller way, and your renter (now there is a gimmiepig if I ever saw one). You are not choosing for your stated priorities.
Your mother has her OAS/GIS/CPP. She is not destitute. She should be paying her way. If I were in the same position I would be. We spend money on our children to get them to the point where they are self-reliant adults. As a mother, I hope my daughter will then do that for her children. So in a sense that is "paying it forward". If your mother were destitute that would be a different story. Fortunately in Canada we do not get hit with the huge medical bills that might be incurred in the US in your situation.
Your niece is costing you - food, clothes, school extra expenses, added utilities, whatever. I am not suggesting you make a profit from her child allowance, I am suggesting you should financially be at zero for her.
Your car is dying, and your renter is driving it - not good. How does he do this? Hot-wire it? If he has keys for it, how come? Get them back. Every province has rental rules, do you know what yours are? Find out if your rent is reasonable - if it is low for your area and the apartment, raise it to what is reasonable. If he is unhappy, too bad, he can leave. If the increase was reasonable for your area, you should be able to get another renter. If the rent is already appropriate, then your renter should stop feeling sorry for himself and your husband should stop feeling sorry for him. And no more car use.
Is your husband on the same page as you are? Or does he see you being a doormat financially with your family members, so he is a doormat for the renter? Remember, if you two work together and support each other, you will both be stronger. An old Roman symbol was the fasces (Mussolini borrowed the concept, hence the word fascist). The fasces was a bundle of sticks tied together - each one could be easily broken by itself, but together they were unbreakable. You and your husband need to be that bundle of sticks, strong!
I have a Canadian family of 7 and 2 dogs living in a 3 bedroom house with just our beds (no fancy bed sets, just box and spring. There is a $70 bunk bed I bought off Kijiji that the kids share. ), a dresser, a love seat, and a dining table.. Our car is breaking down (so far we've spent $1200 a year on it JUST FOR REPAIRS) so we want a new car, don't know what kind to get for the size of our family. We have a meretricious tenant living downstairs that we want to get rid of (like now, because I want to beat him with a mace then drive over him a couple billion times with my already inefficient minivan. That horrible, horrible grump is really stressing me out). Finally, I want to quit my second job so that I can spend time with my family... maybe retire? On average, I spend about an average of 10 hours a week with my kids... how depressing is that? Bad mother. I know, but what else can I do. There's no money. I am sick of debt. I am sick of restrictions.
Wait! There's more!! I can't say no to Granny. It's been ingrained in me that it's a no-no. Add the guilt trips and constant rants you'll get a tyrant that spends A LOT of money that I don't have. Mostly on food, but the problem is she "buys a fancy pen before she learn's how to write" I hope that makes sense. Is that even how you say it? The Mr. is going to laugh at my sad attempts again. OK... so... the finances...
Mom's already got all that coming in. She is paying for life insurance on herself, my bro (against his will) and my niece (no idea why), some to niece's RESP and anything else she may want to buy.
I don't feel that taking care of my niece is a burden. I never felt that way. Her mother helps where she can and I have not asked for her help. I feel that her allowance should remain hers. It's not mine.
Apparently he feels that we're taking advantage of him and he can find rent better else where (although, I told him there's nothing keeping him here) so he's taking advantage of us. Unfortunately, despite my attempts, my husband doesn't feel it's right to just leave him in the cold. Considering his ungrateful nature, I don't have sympathy.