For the Mort Myre coordinate clue at 05.37 N 31.15 E, the coordinate guide says: "Mort Myre Swamp, on the Nature Grotto island, just North of the tree. You must have started the Nature Spirit Quest to get into Mort Myre Swamp. If you bring food, bring druid pouch(es). Saradomin wizard will attack. Note: You cannot use familiars on the island, as it is a Summoning free zone."
Whether it's a glitch or just an update, I'm not sure, but it looks like you can bring familiars with you now.
- Serpent Eye