Thank you for your question
My name is Clare
I shall do my best to help you but I need some further information first
Do you actually ever envisage the loan being repaid?
Then there are two choices, either ask your son to sign a Declaration of Trust confirming that he holds the property on trust for you both in whatever shares are agreed; or you can have a formal charge over the property - like a second mortgage.
Since it is a loan which is repayable this will not be relevant so fat as Inheritance Tax is concerned the outstanding amount will simply form part of your estate
Please ask if you need further details
No you do not need both
You can deal with the form yourself if you wish!