Don't always believe what google finds that is for real, there is so much conflicting info across the web :lol:
All in all a cichlid is a cichlid... no matter how peaceful a cichlid may be, towards each other through spawning... towards their babies raising them.... they will always get agro when it comes to defending their young... Keyholes are relatively peaceful but they are only doing as VM said, protecting their brood.. it's natural.
You don't really have any other option than to find them a new home or get yourself a new tank, if you are planning on keeping the pair.
They don't see it that your other tankmates had the territory first, they will see "oh we have a breeding ground... this needs to be our territory so look out".. fair enough