I read over grappling in the Rules Compendium, and it states that you can ONLY do the actions listed in that section, and for attacking it specifically only allows you to attack your grappling foe(s). So the answer to 1 would be no.
For 2, EBT sounds like each tentacle counts as a separate grappler, especially since they function as such. So no, it would not be a 3-way grapple.