A high edge cat box is the best litter box for buns – they like to back up to the edge and pee with their butts in the air so they don’t get it on themselves, so if the edges are too low… the floor is going to be where it goes. Use only a small amount of litter in the box so it’s not too high so they can get over it as well.

For outside… my male does that too sometimes, he’ll occasionally mark it as his with some droppings. I just clean it up and deal with it, not sure what sparks it, he’s even replaced them when I cleaned them up before right in front of me. My female will only do it if I accidentally spill a piece of her dirty litter on the floor and it smells like her toilet. *shrug*

I would try using two litter pans, one for each bunny, and see if they like that option. Also agree with a high backed pan as well. That rim of your current pan might be better if removed, so they don’t have to jump over it to get into that pan. Use that one, and get a second high-backed one and see who goes for what.
Also, clean the area they peed on outside the pan with white vinegar and water to get rid of the smell, or they will continue to return to that spot.

Some bunnies prefer soft to pellet litter (Equine Pine is a good pelleted litter btw) so one may be objecting. If they both used it well before, no need to change, but if not, you might try something like Aspen shavings, Yesterday’s News or Carefresh litter which is softer. Little changes in litter and pans make a big difference to bunnies. Be sure they are located in a spot they like, too. They want to feel safe, so pick the side of the closet they want to go in.