I had pm too - just to say info had come from a rellie.
Have also asked for info to go on to here, not via pms.
So, it could be there are no sources, just family hearsay.
In whgich case we need to start with something more concrete and work back. These people are said to be great aunt and brothers. So there should be another sibling who is op's grandparent - perhaps we can find the family fron there. But, of course, need the info first!