What your lawyer in Puerto Rico is likely familiar with is the most common situation in which a resident of one of the US states dies and the executor or his or her lawyer files the Will for probate in the deceased's home state, and gets it admitted to probate there with Letters Testamentary issued to the Executor. Typically a Will that complies with the applicable laws in the state where it was executed and witnessed (in your case California) will be acceptable in all other jurisdictions.
However, as the deceased's home state probate court has no jurisdiction over any real property owned by the deceased out of that home state, it's then standard procedure for the named executor (or a lawyer for the executor) to file for "ancillary probate" in the jurisdiction in which the real estate is located -- which essentially is an abbreviated process in the new jurisdiction to have the probate court there accept the Will for probate, and issue Letters Testamentary and authorizing the Executor to sell the local real estate.
In your situation what is involved is original probate -- in Puerto Rico. It's just as if the deceased made a Will in California and moved to Puerto Rico and never made another Will.
In that case it becomes incumbent on the person presenting the Will to prove to the Puerto Rico court that the Will was valid under the laws of the state where it was executed (here California). The Puerto Rico court (and your lawyer) likely does not know if California (the state where it was executed) requires 2 or 3 witnesses, or whether the witnesses have to see the deceased actually sign, or if s/he might have told them after s/he signed it please be a witness, or if they have to be "disinterested" for example to make sure that they wouldn't get more under the Will than they would have if there was no Will?
And your Puerto Rico lawyer -- and the judge, may not know what those rules are. Had the Will already been admitted to probate in the state where it was made, there would be no remaining question as to whether it was properly executed and effective as a court would have so found.
I suggest that your Puerto Rico lawyer should consult with an experienced California lawyer to determine if the Will appears valid, and find out what it would normally take to have it admitted to probate in Californi, such as affidavits from the persons who served as the deceased's witnesses when the deceased signed the Will, unless there was set of proper "attesting" affidavits attached to the original Will. He should also likely get an affidavit from the California lawyer stating that in the lawyer's opinion the Will appears to be in proper form and would qualify for probate in California. The Puerto Rico lawyer would and present that together with whatever additional proof is necessary under Puerto Rico law to have it admitted to probate.
