Hello and thanks for using Just Answer.
I am Al and am happy to assist you with your enquiry.
As you currently hold the property as Joint tenants, the property will automatically pass through survivorship to your son, if you were to die first. Hence, the property will not form part of your Estate and any clause you put in your Will concerning your "share" in the property will be invalid.
Therefore, you need to convert the way you are holding the property so that you and your son hold it as tenants in common. Only by doing this, can you guarantee that your husband has some security to remain living in the property, if you were to die first.
By converting the property into "tenancy in common", you can still leave your half share to your son in your new Will, but you can also put a provision in that while your husband wishes, he can remain living in the property, paying £x per month in rent/maintaining the property/and paying all outgoings and Buildings Insurance.
If done, your son is then prohibited from being enetitled to demand a sale, while your husband wishes to remain living there.
The one thing you won't be able to make legally binding is your wish for him to be able to rent out part of the property/take in lodgers and retain all the rent. This is because, legally, your son is entitled to receive half of any such rent, as he is the co-owner. Therefore, the best you can do in this regard, is put a letter of wishes with your Will, which is a separate non legally binding document stip
ulating that it is your wish that your husband be entitled to retain all the rent. It would then be up to your son whether he abides with your wish.
The Solicitor who prepares your Will will also be able to deal with the necessary Land Registry form converting your ownership into tenants in common.
I hope this helps you and answers your question.