It's not unusual for anyone to look for money inside a property,be it hidden,or readily available. When there are relatives looking for the same thing,it's a case of whoever gets there first.
My late husband did the same when his sister died. He knew there'd be money somewhere because of rents from properties,and he'd wanted to find it before anyone else did.
However,when it was finally found,his nephew was with him at the time,he was obliged to split the contents because of it being an intestacy.
Needless to say it was kept quiet and not added to probate.