Coercive control

www.ageuk.org.uk/information-advice/health-wellbeing/relationships-family/protection-from-abuse/

There is a phone number on the age uk site.

If you report it to them, I'm sure they will take it seriously.

This sounds horrendous for you and I'm sorry I don't have an answer.
All I can think is that you must get help for your Dad from somewhere - but where? You've already tries S Services and the police and while I can understand the police not being able to do anything I'd have thought social services should have been the people to do something.
Do you know (or can you find out) who's his GP and try to enlist his/her help? Could AgeUK help in any way?
I know your Dad won't like this - but would he go into a Home? They are quite safe now and don't take new inmates without testing, but although they'd offer safety and peace for your Dad I can't see him wanting to give up the Independence of his own home.
Incidentally have you got Power of Attorney?

Message withdrawn at poster's request.

could you go look after him, live there, or have him move to near yours.
who controls the money.
request a social services assessment as dad's needs have changed, and you are concerned whether present situation is safe. don't mention brother.
you would need to attend this ideally.
you could consult an expert, eg lynn phair, if you have the money.
why can't brother live there eventually. is house rented.

also try to get an Occupational Therapist assessment.
there are community ones, local to his home area.
if stuck, try write to his GP to request Occ Th, re safe environment of home.
get as many profs involved as poss. don't mention what you most fear, brother, as that has not run.
talk about safe environment. adaptions may be needed. other support services. take a wide view.

Good advice - not to involve your brother just yet. It could be construed as sibling conflict.

Sad situation. It happened to my parents. We had to call police when the woman started to answer parents phone and not let us speak to them. It ended up at a solicitors before they lost their house. The woman's family name was on all documents relating to sale of their home. We stopped it just in time. Parents both now passed away. Our mums money from house sale paid for her care home fees after he died

sadly, this sort of thing is much more frequent than good people would imagine.