Legal Question in Wills and Trusts in California

Yes, but I would protect myself with a signed affidavit from the patient's attending physician that the person was lucid during the interval in question.

Mr. Seidler is correct. The individual may be legally competent to sign legal documents and to write checks (presumably to pay his/her bills) even though he/she suffers from Sundowners. Sundowners is often associated with dementia. Individuals in early stages of dementia, and sometimes even mid-staged,can be legally competent in the type of transactions you describe. I highly recommend that the individual be evaluated by his/her doctor prior to signing any documents. During the time of the signings,the individual should also not be receiving any medication that would interfere with his/her understanding of what transactions are involved.