It would be possible to come a third yamaoka killer?

I think this somehow depends on the Japanese commuity's enthusiasm

Maybe Rin's father?

Possible, but unlikely. Having two killers that were from the same heritage was awesome but three would be taking it too far. They would all kind of blend together and lose their unique features. I wouldn't want this and would much rather have an entirely new killer. As I said though, it's unlikely that this would happen

I'm not trying to see DBD turn into an all-out anime so I hope not. I'm personally not interested in a third Yamoaka.

I think it's far more interesting conceptually when DBD constantly strives to make their characters unique as possible from all different kinds of cultures where different urban legends and horror myths were created as original reflections of those places and the things those people were afraid of.

So you'd see why I'd be a little miffed if DBD all of a sudden started overusing the Yamoaka bloodline taking up all the resources that could instead have been used for wildly different and unique newcomers instead.

More of a practical (opinion) response rather than a lore based response, but I felt it needed to be said anyway.

EDIT: (Lore Based Response)

I did some more digging, and I found that this is actually just the traditional Japanese Sword Display. We here in the west think of Knights with individual swords that are given names and personalized. But in Japan Samurai warriors normally possessed three "swords" The Katana (the widely recognized full sized Samurai Sword), the Wakizashi (a mid-sized sword which resembles the Katana just smaller), and the Tanto (the shortest of the three which was more equivalent to a survival knife).

These weapons were placed in display stands in descending order with the shortest on the top and the longest on the bottom. However, there are cases of two-tier displays:

"In the case of a two tier stand that has a shelf instead of a third tier the correct order would be the tanto on the shelf. Katana on the bottom and then the wakizashi would be on the top."

TL;DR. I think this is just the Oni's weapons passed down, they don't belong to multiple people just to one. Kazan Yamaoka. When he came to the realm of the entity he took one of his swords to use and left the other in the display case which we can see in the map.

I think 3 yamaokas would be too much imo but I would like another new killer who's connected lore-wise to one of the killers we already have.