Do your Gravenstein's have fruit? I don't remember all the technical terms, but the gravenstein will not pollinate another apple tree. It is an early bloomer. Honeycrisp will pollinate others but it is a mid to late bloomer. You need to have the bloom times overlap. With a gravenstein tree, you need a tree to pollinate it AND another tree to pollinate that pollinator. Here is a webpage that mentions some of this.

http://www.raintreenursery.com.....apples.htm