I've done some research and I'm not sure, is the answer - Rheinische Schattenmorelle is a sour cherry and is self fertile - Hedelfingen is not self fertile, will need a pollinator nearby, and two of the same variety cannot cross pollinate, but the other cherry you've bought is not mentioned on the list of possible pollinators. Hedelfingen is a mid to late spring flowering one, as is Rheinische - suggest you wait and see what happens in year 2, by which time you'll know if they flower together or not, and hopefully whether they cross pollinate, though that's obviously dependent on when each actually starts flowering in terms of maturity.