We have two bathrooms in this house (such luxury, oh my gosh, I grew up with one and there were five people trying to use it all at the same time) and sometimes if we've got guests that really need to use the bathroom but the hall bathroom is occupied, I'll let people use the one attached to the master bedroom (and yeah you have go through the bedroom for it but I try to make sure it's not an embarrassing wreck for either of us).

This doesn't look like that situation. Jon needs to boss up a bit and start respecting private spaces. (Model some boundary enforcement for those children!)