The thing that really bothers me about this sort of arrangement is that it seems to heavily depends on a the sale of a home in Europe from a relative (presumably a parent), that happens at a later date.

To me, the money that is earmarked to be used to pay for the second mortgage doesn’t appear to be “guaranteed”. What IF the OP can’t get $150k out of that home sale in Europe? Then what?

In the past I took out HELOC’s on my primary up to $200k to short term finance my rental property purchases. But I only did so, because I knew that worst comes to worst I could pay them off if rates rose suddenly, and I knew I could refinance the condos into a fixed 30 year loan after closing escrow after the waiting period.