They are the children, relatives or apprentices of an former party of adventurers that have by and large retired or have been killed. It therefore becomes natural that they might be gathered to attempt a to form a second generation of that same party.
I would have the local survivors of the former party around to act as mentors, role models and the source of an occasional hand if your players' characters need to be rescued or ransomed. I would not make them too high level (4-8 perhaps) so their capabilities are notable rather than awe-inspiring.
If you adopt this I recommend you work out what ended the adventuring career of the original party and make up character sheets for them using the rule book guidelines on creating experienced characters. Perhaps there are some matters left over that will warrant the new party's attention at some later date.
You could have local landmarks bear signs of their experiences like the place where the houses that the vengeful dragon burned down but which were never rebuilt or the temple built around a fabulous altar stone brought back from an expedition.