Welcome!
There are many yellow cichlids. It could be a dwarf, could be a lab, or probably others equally different. Post a picture of them, or post what they are to get useful replies.
Also, a baby jack dempsey will almost certainly be eaten by the other dempsey or potentially any other fish in the tank. People will need to know what size the fish are if they are to give you advice.
Lastly what size is the tank and how long has it been running. Do you plan to upgrade the tank or do you have another larger tank available?