Can a Remove curse spell be cast on yourself? If all allies of Von Richten are cursed for helping him in Curse of Strahd, why does he just cast Remove curse on himself?
Yes, Remove Curse most certainly can be cast on yourself. This QA (pointed out by NathanS) says that you can target yourself if a spell targets a creature of your choice (unless the spell specifically states otherwise). This is also confirmed by the Player's Handbook under the Targeting Yourself section in chapter 10. Remove curse has a range of Touch. The description of the spell states (emphasis mine)
At your touch all curses affecting one creature or object end.
As for the second half of your question, I can't answer that as I don't have the book but maybe someone else can who does.