So just to clarify this ability with everyone.
Assuming that Hostile Takeover was done early in a round, the wording states that it performs its TURN as our ally. But at the same time, it doesn't state that the ally status ends right after.
My group's logic is that it is a persistent effect for the rest of the ROUND since you put a character token on the enemy to signify the status. Thematically, it doesn't make sense that the other monsters post-Takeover in the round wouldn't respond to the attack and see the "ally" as a threat and re-focus its attacks for the round.
No, this is really wishful thinking. The monster simply performs its turn as if its allies were its enemies and its enemies were its allies; nothing is said about its affiliation being changed in the view of other figures.
After its turn, everything goes back to normal. The wording would be very clear if this wasn't this case (e.g. it would say "For the entire round this monster is treated as if... instead of the current wording).