The trustee can do whatever the trust allows. So if the trust allows a sale of the property, then this can happen. If the trust allows the sale of a property to the trustee, then no problem.
The issue here is that he technically has to SIGN OFF on any such sale. But, if the beneficiary does not have an understanding of the contract, then their signature is invalid. People v. Lara, 432 P. 2d 202 - Cal: Supreme Court 1967
Now, the signature is PRESUMED valid until challenged/proven in court as not. If no one is going to challenge it, then it should not be an issue, but TECHNICALLY someone who is COURT-ORDERED as the GUARDIAN for him should then sign off.
Now, the actual purchase of a property is quite simple. All one has to do is to transfer a DEED from the TRUST (seller) to the TRUSTEE (buyer). The problem here is that when there is a trust involved, there is a lot more paperwork. So one WILL NEED counsel here. It is virtually impossible to do this otherwise, especially from abroad.
May I recommend the CA Bar referral program - here
. The attorneys are vetted and qualified. You should be able to find an attorney you are confident with and whom you can trust, and who is available ASAP.
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