Can alien Grey/human hybrids and human clones born to impregnated human mothers mate and produce young of their own?

This does not happen. This is not the intention. These beings are designed to intrude on human affairs, to act as a substitute for human young to satisfy the parents they are propagating and fulfilling their desires for offspring, and duping them into accepting these alien constructs as their own children. This allows infiltration as a covert attempt to gain entry to human spheres of influence and be positioned as agents of change whenever desired by the Extraterrestrial Alliance. They may turn on their parents and kill them. They may do damage elsewhere as instructed. And in particular, they displace potential human young who otherwise would be born to those parents, but who will be misled in thinking they have their offspring, and there may be more than one alien being implanted to round out the family as desired by the parents. This achieves the second goal of the diluting the ranks of humanity and shifting to alien originated beings.