Hi Sarah, I knew Jean well, what a kind, gentle woman she was.
The last I heard was that the children and I presume Dimitri were somewhere in Northern Greece. Remember that "the children" would now be adults and realistically could be anywhere.
I fear it would be an onerous task to seek them out.
Maybe...just maybe someone on Symi may still be in contact with Dimitri.
Perhaps a plea in the Greek section of Symi Visitor?
Good luck, Sarah.