hello, anon(s)!! these are some excellent questions & i'll do my best to tell you some useful & coherent information on the subject:
ie Catrina's magic depends highly on the well-being and happiness of the souls in the land of the remembered - higher their spirits, more powerful she becomes; though she can't use her magic to hurt anyone. that's like THE LAW. Xibalba, on the other hand, gains power in misery and the felling of helplessness etc)
SO. about the travelling thing: both of them can pass through the underworld realms, though the action itself slowly sucks the life out of them - the bond with the dead lands becomes stronger every time they cross the underworld's border. of course, the dead keep their secrets & artifacts which both Catrina and Xibalba would like to own, but the price of searching for them is often too high
(also Manolo and Joaquin aren't the only familliars they own, the more channels one has, the tighter the bond with the dead lands)
(2) RESIDENT MAGICIAN: San-Angel had never belonged to any of them, though Xibalba showed up there a couple of centuries earlier. The resident magicIan(s) (a dynasty of them really) of the place prefer to keep neutrality, since they're not interested in the DEAD people
(3) A HEALTHY RIVALRY: They don't hate each other, though have a very little respect for each other's methods/interests/hairstyles. also Xibalba wasn't very friendly towards Catrina during their first meeting so.. the bad first impression was left.
