A cray is a possibility. You could even get a few.
One thing to note about crays is that you have to make sure they're large enough so that they do not become food for your fish when it comes molting time, and that they're not too large that they try to pick the fins of your fish.
I believe the pleco should be fine, and from my understanding, Dempsey's are pretty fiesty, so I think the cray would be the thing that should be watching out, rather than vice versa.
As for the Parrot, I am assuming you mean a blood parrot? The hybrid type? If that is the case, you should not have to worry about the parrot bothering the cray due to its mouth being so small and being unable to attempt to eat the cray.
As for the Jack, I think he is going to be the real damper on the potential tankmates for your tank. Jacks tend to be territorial, and can be rather aggressive. Your option could be to attempt to get some other cichlids for the same region that the jacks are from, but it is very likely that he might bother them and even attack them. Truthfully, I'm kinda surprised the jack hasn't bothered the parrot yet. Although I have not had experience from the jacks myself, I have heard some nice horror stories about my dad's jacks when he used to keep 4 of them in a 100 gallon.
Hope that helps. Feel free to hit me up on AIM if you want.