Legal Question in Criminal Law in California

Evidence may be suppressed by appropriate motion for 'good cause' if justified. Whether it will be is up to the judge. If you are facing criminal charges, and don't have an attorney, thinking you can effectively defend yourself by asking for hints and tips here, you need to rethink your position. If this is in CoCal courts, and if you get serious about getting legal defense to try to keep you out of jail, feel free to contact me.

Your relative's dementia does not strike me as good cause to exclude the statement. It's a reason to doubt the statement's accuracy, but that goes to the statement's weight (meaning how much a jury should rely on it) rather than its admissibility. If the D.A. uses the statement you can try to show that it came from someone with dementia, but you probably can't prevent the D.A. from using it at all.

There may be other reasons why the statement would be inadmissible, however. Statements made outside of court are hearsay and are inadmissible unless they fall within one or more of the recognized exceptions to the hearsay rule. I do not have enough information to say whether this statement would be admissible or not. Either way, though, your relative's dementia is unlikely to be the deciding factor.