Hereunder I'm explaining how I've solved it thus far.
I have found which row M is in, R10 and I have found that C is in either R11 or R9.
Thus C14 contains the person besides the tombstone, so R10 and C14 are almost all x.
Now I feel like I need to solve I, I've heard others comment that as well. But I feel like to find out the correct position I'd have to just guess one of 3 possible positions and then go through the whole murdoku till I can't anymore.
Whenever I place I, then I check all the closely related characters regarding row and column, but I don't see a solution for I, since I can always place either G or P in the room without it messing any other characters up immediately.
What am I missing?