Should a child be responsible for their parent when they get older?

I’m not really sure where to start with this.
I apologize for the long post. I’m not sure if it makes sense and if it’s all relevant.

I am a 36 year old married mum of one.

I moved out of home at 18.

Things have recently blown up with my parents (my mum in particular).

Dad has recently found out he has some heart issues, he is 69 in October.

My mum has made remarks prior to that diagnosis that she “didn’t know what she would do if something happened to my father” (I always got the feeling that she expected me to say it’s ok mum you could come live us) and with this diagnosis my mum has become even more stressed about what she would do. I said to her a few weeks ago that they should make some plans so she will be sorted if something happens to dad.

On Sunday night the conversation about what would happen to her come up again and this is something I’ve been stressing about for months, it has been eating away at me. I’ve previously told my husband that my mum would have to come and live with us, his response was “if she moves in I move out”.
So mum once again said she was worried about her future and I replied that I had no room for her (I have a very small house, I do have a spare room but my husband and I may have another baby). She did not look happy about that comment and my dad laughed and said “you would have to build her a room” (we are in no financial position to do that!) Then I blurted out that if she moves in my husband would move out. They do not get along. They have both said and done things that have upset each other. My mother has disrespected my husband in his own home. (My husband has admitted that he is not innocent in the situation) Her reply was “so you want me to end up on the streets” and “I’ve looked after you your whole life” she didn’t seem to care when I said my husband would leave me.
My mother and I don’t have a good relationship either. Yes I feel awful for blurting out what my husband had told me. I could have said something nicer.
I fully admit I’ve got issues but anytime I tell her that she has behaviors she needs to work on she turns it back on me, like it’s all my fault.

My parents have a mortgage on a house. My parents got a mortgage when dad was in his mid 60’s, he used 2/3rds of his super to get this mortgage. They have made some awful financial decisions and have had debt collectors chasing them. They were always upgrading their cars every couple of years. Mum hasn’t worked for quite a few years.

They can’t sell the house as my brother lives in it and the market is not good in that area so they wouldn’t get the money they need for it.
My brother won’t be able to take my mother in as he has no job and they would lose that house if something happened to dad. I refuse to take my brother in as he sexually abused me when I was 8.

My mum still treats me like a child. She is in my opinion a narcissist. When I talked about having another child she said that was not a good idea as I couldn’t handle the one I had. She did help me out when I first had my daughter as I struggled a lot (my husband works away every 2nd week) which I’m grateful for. She always brings up how much she helped me. She is always telling me “she bends over backwards for me”

She would babysit my daughter a couple of days a fortnight while I worked. I have not paid her for it, she was kind enough to do and I would thank her for doing it and I’m grateful for it. She has regularly called my daughter a pain in the arse “jokingly”, she always gets cranky at my daughter for making a mess, she is not even 3. She gets cranky when my daughter doesn’t make it to the toilet. I’m now at the point where I don’t want to leave my daughter with her. She once left her in a dirty nappy for over an hour when I was asleep (and did not try to wake me). But then is the first to get cranky at me when I don’t change my daughter immediately.

She constantly picks on me. Criticizes my parenting. Try’s to give financial advice. Doesn’t respect privacy. For example my sister in law got a redundancy and my mother asked me how much money she got, I told her it’s none of our business.
I used to talk to her about everything but now I don’t want to tell her anything. I feel like she thinks because she is the parent and is older (I wouldn’t say wiser) that I should bow down to her, like she is the superior adult. That I’m the child and I know nothing, even though I’m 36 and have a relatively successful life of my own.

If my mum moved in we would lose a lot of our privacy and even though she is in ok health now what happens when she gets older and we want to travel. I would eventually become her carer. She was her mother’s carer for a few years and she struggled with that. Can’t she see how much she is asking of me?

I feel like my mother and my husband have put me in a really awful situation.

Is it up to me to take my mum in if something happens to my dad?

Thanks to anyone who read to the end 🙏🏼