The aggression and intimidation are 100% unacceptable
But speaking as someone who, for the best of intentions felt obliged to 'help out' older family members in my early 20s with loan/money/mortgage arrangements - being tied as adults into family finances is a recipe for disaster for everyone, both financially but also with relationships.
What seemed reasonable at 20 was certainly not OK at 27 when my life had moved on. I was in a relationship and we were thinking about our shared future/children - but my finances were tied up together with family investments, 200 miles away. So I had lots of financial obligations with none of the control of the day to day - and despite requesting an end to the situation/house sale to allow me to move on, buy a place to live in and so on, this wasn't a priority for the others, who were receiving the benefit of my money and credit being used, and quite happy with the situation. They could express apologies and guilt about it, without ever acting to sort it out - they couldn't see what difference a few years might make to it or me.
I did not become confrontational with them due to the distances and I couldn't see how it would help. Seeing each other infrequently meant I was able to keep the emotions out of the business, but it was a huge stress that gradually dominated my life, I felt resentful that despite my good employment and earnings I was struggling due to the extra drain on my finances, angry that I missed good opportunities to invest and save because my credit and money was tied up in their plans, missed out on first time buyers assistance, had lots of time to brood over it while on maternity leave in shitty rental flats, when served eviction notice at 5 months pregnant, while searching desperately for a new place to avoid my dc moving schools, being unable to make a real homely environment for the DCs. It certainly put strain on my relationship with DH and our financial arrangements in those years - we couldnt 'Leave and cleave' eg become a proper adult partnership making decisions together, because a lot of my finances were entwined with other peoples.
Eventually DM, who understood my side, intervened. Arguments were had, the situation was sorted, place made ready and sold. The money came to me, and I shared out exactly what had been agreed (apparently some people were nervous that I might 'cheat' them by keeping the money which is definitely one of those 'Every accusation is an admission' moments, but it wasnt even tempting, I just wanted the situation over after 10 years in all)
Within a day of receiving and sharing the money I got a phone call from 2 family members who had already mentally spent my share for me in their schemes- 'What you really want to do with the money is....' And at that point I went fucking ballistic, explained that I had had absolutely enough of them and their shenanigans, that my savings and credit rating were not a resource for them in any way, and that what I needed was a house for my own family, and to be able to get on with my life and priorities. It has left a degree of bitterness and certainly impacted how I feel about them, and how I will deal with finances in the future.
What I am trying to say is that you need to disentangle your finances from your son and make an end to this situation as quickly as possible and he can. I am sure, like my scenario, all your intentions were good, but then life, illness and changes got in the way, and now its not working for anyone. Hes certainly treating you badly with his behavior, but you are not treating him well and if it goes on too long unresolved will be hard to come back from.
I would suggest sitting down with him, put all the cards on the table. He needs to grow up and stop making ranty demands especially when you are ill, but you need to hear his side too. Hear him out, where he is at/and what his stressors/plans priorities are, and share yours, stress, chemo, warts and all, explain the pressures you are under. It might be very uncomfortable and air a lot of resentment on both sides but hopefully you all can come to a shared understanding of the situation, apologize to each other for the last few months, and make a realistic plan for how to disentangle everyone and move on.
And never blend money and family again, unless by gift giving of sums you can afford