So my players have just made it to Vallaki last session. After the Madame Eva reading they learned a man with a funny monkey (Van Richten) is their ally, and the tome is in a wizards tower (Van Richtens tower).

Also two of my players are rolling new characters, one left the party after becoming too evil, the other a new player. They both are sisters in game, and have chosen a homebrew race called blood cursed. Both of them have had the curse of lycanthropy passed down from generations. They came to Barovia after looking for rumors of their ancestors being from this land. Both of them see their beast blood as a curse and wish to end it. We've made it so they cannot or perhaps do not transform at will, but only on a full moon or if the change is forced. They are trying to do what they can to not change, but still in human form have some benefits such as a claw that does extra damage but also mildly injures the player when used.

My question is how can I have these two lycanthropes and Van Richten coexist in the party? My thoughts are perhaps he is aware of this curse and through his studies has himself tried to cure it. Perhaps he is their best lead to curing themselves. Van Richten could even view them with pity, and try to help them avoid a full transformation. Obviously if the change does happen he has to put them down, a fact he may or may not tell them.

Another idea is perhaps he was once friends with an ancestor of theirs. Maybe he tried to help this ancestor and failed and was forced to kill him or her. This weighs on his mind, after all Richten was a doctor before he became a monster hunter. I'm not sure if a cure is possible in the base game rules, but I would prefer to be able to homebrew something, obviously for late game. Perhaps killing Strahd somehow ends their curse.

Any ideas are appreciated. I know I've asked help on here a lot and I always enjoy the feedback, this is a helpful and great community and I appreciate you all making me a better DM.