Hello I am a solicitor with 20 years experience. I will try to answer this.
Methods that could be employed to archive this outcome include granting a life interest to him in your will with the property going to the others or their issue after death. It might be that the life interest could be conditional on the payment of regular sums to his siblings, or perhaps that the other siblings could receive more elsewhere in the will to make up for him getting a life interest on the property. You could also give to the 3 of them jointly and make it clear what his intention is for the property and hope the others honour it but this wouldn’t have legal force.
Another possibility might be to grant your son a tenancy which will continue after your death. Then you might be able to bequeath the property to his siblings effectively with him in a status similar to a sitting tenant.
This is a complex area of law and whatever you decide must be drafted very carefully. You really must see a solicitor face to face in the orthodox manner to prepare a will that deals with the all the issues. This is not something that can be done property through this question answering service.
Your suggestions are similar to what I have been thinking all along. What I need to know is; if I bequeath the property jointly to the three of them, and grant a lifetime tenancy to my resident son with him paying rent to the other two, can this be made to withstand an application to overturn my will and evict him.
The law in this area is way to complicated to be dealt with in this forum. I have helped you to the extent that it is possible to do so in this forum. You need to instruct a solicitor to make sure that everything is challenge proof. Ther is no other way.