Buying property with multiple owners

Sorry but your post does not ask a clear question

Example:    “To do a notary'”.  That has no meaning

Instead of me guessing what you want to know, it would be better if you explained the situation more clearly

Hello,
I was referring to buying a property belonging to 4 Spanish brothers.upon investigation it appeared one of the brothers listed as co owner passed away a year ago.he has a son who has not officially inherited his father's asset .he wants represent his dad's percentage but cannot sign in an official capacity.he needed to apply for the deed to be changed into his name.
I do not have funds to extend my stay or return sign the property from them when his paperwork will be ready. So it was suggest that I go to notary and sign with the remaining 3 brothers totalling 75% share but then sign a private contract recognising the heir to the deceased to prevent hello him from refusing to sell is 25% share when his paperwork is ready.
The point is I intend to collect the keys on the day of notary with the he 3 brothers .be in n the property whilst waiting the son to complete his request inheritance transfer of ownership from his dad.
Is this safe practice?

I do not think the transaction can proceed unless all he owners have legal possession.

However you can give power of attorney (poder) to someone who can then sign for you when the transaction can proceed.  You do that before a notary. The person you nominate does not need to be present at the time you make that document.