It looks like a type of plum tree. If I am correct in my id the fruits are delicious.

could be crab apples going by the reddish foliage. Cut one open if it has a core then its an apple if a stone/pit then a plum [or cherry].

You can always make jellies (pipless/stoneless jam- this bit is for those of you not in the UK who may call preserve jelly something else!) with this type of fruit. Most of the libraries have books on jam making - or the jolly old internet of course!

My guess would be crab apple for the green leaved one, and cherry-plum (Prunus pisifera) for the red-leaved.
We have cherry-plums growing wild in the hedges near my house, and while you wouldn't buy the fruit, it's pretty tasty straight off the plant, just a bit sharp.