If you work it out, there does seem to be time for Richter to be Reinhardt Schneider's grandfather.
Reinhardt looks to be at least in his late twenties (and that is being kind to him) in 1852. For the sake of doubt, let's set his age at 25, putting his birth circa 1827. If his parents (one of which would be Richter's daughter) were no younger than 16 (reasonable or not given the date? people sometimes got married very early back then...), their birth dates would be circa 1811, at which time Richter would be exactly 37 and certainly still able to father children. Even if you fiddle with the unknown ages quite a bit, there's more than enough of a time window.
In my fanfic I placed the birth of his first child (a son) at 1807. Seems to work out surprisingly well with this
BTW, I intend to tell the story of the Hunter Whip's creation in that fic, and give it a plausible place in the Castlevania universe (one that doesn't ruin the essence of the canon). Let me know if you ever make a genealogy that expands into fanfic characters
But if you accept that the Hunter Whip really is different from the Vampire Killer, which I myself now do (and I thought I'd be the last person on earth to argue for that...), then there's no problem with having Reinhardt "borrow" the Vampire Killer for a quick quest from the Morrises or whoever was holding it at the time. Maybe there were extenuating circumstances which prevented them from helping out at that time
I'm just happy to see the non-canon characters getting more mention lately. They're my favorites.