He comes to your house and goes through your post? Why would you put up with that?
Please tell a relative that you trust and also your children about this.
Does he do this in front of you?
or did you see him doing it?
or Did he ask your permission?
That is such a huge financial risk. A person who has access to your post could mine it for all your account details for all sorts of things and take out credit in your name.
Stop asking him for financial advice and see an independent financial advisor instead. NEVER use his "financial advisor" that would be crazy.
He could be completely genuine.. or he could have showed you his "portfolio" and deliberately left you alone with it so that you would peek and think his "investments" were doing really well.
He already knows you have 1) an income, 2) 11k savings, 3) an inheritance on the way and also 4) possibly a lot of equity in your house - if he had seen your mortgage statement he'd know exactly how much cash you are likely to have if you sell.
Put your post away and have a lock for your filing cabinet. Change your passwords and run a credit check above all tell your family.
If you have two DC at uni... they will be there for 3 to 4 years. They will still need a home between terms. When they graduate they may want to do further training or it may take a long time to find permanent jobs on starter salaries with student debt. There's a housing crisis. They may need to stay with you for a while, whilst they get on their feet and save up to pay for their own place. up to two years is not unrealistic in this day and age.
Why would you give up your home, which will appreciate in value, to start subsidising someone else's home "proportionate to income" when you could use that money to start paying down your own mortgage instead and keep some security for yourself and your DC? If you have to move, don't sell your house - rent it out.