I did ask for some proof yesterday, and from a fast paced response to my other emails and questions, this last one I asked has yet to get a reply :-)
Yes, I agree about the ethical aspect and that is more important. Him claiming he owns it is a tough one to accept without any trace.
Looking over all of them now, I just found one of the images he sent for retouch has the name of the photography company that did the work!
It looks like he screen grabbed from the photographers site and missed cropping out the url on the one image :-)
So I just emailed the "client" to help me understand how you own them, and I added that if you don't, to contact the photographer and offer some money to allow you to have them in the low/1080 resolution you need for a family slide show(his original explanation on his needs). The photographer has no use of the images, so offering him half the cost of what it would take to remove the watermark might get him to let you have them. Tell him to put his watermark on the lower corner of the company name may also help
Lets see if that gets a reply email :-)
Another thing I can do is contact the photographer and ask him what to do :-) ?