Legal Question in Real Estate Law in California

If one of three joint tenants properly deeds their interest from themselves as joint tenant to themselves as to a 33-1/3 interest as their sole and separate property, that will sever the joint tenancy, leave their 1/3 interest intact, and by default will make all three owners tenants in common. That will not, however, have any effect on the other owner's efforts to evict anyone. Whenever an elderly person signs over property to a relative other people can cry coercion or other undue influence. Whether that has any traction will depend on the facts and evidence. However, deeding property to ones children while you are alive is 99.9% of the time one of the most foolish things you can do, because it has all kinds of terrible tax consequences when compared to other ways to pass property to their children. Without more information I cannot even begin to recommend a good method for the parent to try to block the other owners from evicting the son, or whether they even have any right to try to do that or not. But I can assure you that the options mentioned in your question are almost certainly a really REALLY bad way to go about it.

If the son has the permission of the father who is a JT to be on the property, I do not see how the others can evict him, since all three joint tenants have the right to use the entire property as each owns the entire property, subject to the ownership of the two other JT's. The JT can be severed by actions, not just a written document.

The joint tenancies are easily broken and turned into tenancies in common; as Mr. McCormick says, if any one of them decides to go tenant in common and get rid of the right of survivorship that goes with jointtenancy, all he has to do is record a prooperly-executed instrument and that makes all three tenants in common. However, other than eliminating the rights of survivorship, not much else changes. All three remain 1/3 owners and all three have the right of possession of the entire property.

The son can't be evicted if the father wants him there, and this is because the father has the right of possession of the entire property (as do the other two owners, simultaneously) and can install his son as his guest or tenant. This is the same whether the three owners are joint tenants or tenants in common.

Giving an interest to one's son, inter vivos (while living), is a bad idea, partly because the son will get a step-up in cost basis if he inherits, but not if given a gift during dad's lifetime. The step-up will usually reduce the capital gains the son must pay when he eventually sells.