Yes you can use them..but like other crab apples there is not that many uses for them. You could try making crab apple sauce..but you may need to put much more sugar than in normal apple sauce..try combining with some other things like black berries or other wild 'things'.
As for ripeness..if you wait for another month so so..perharps untill first frosts..that should bring out the natural sugars..in theory ::)..they will never be sweet but the natural sugars may make them sligtly less tart.
