Welcome to the group! I'm not an expert on IRNs but any time a parrot shows jealous behavior or aggression it's likely that breeding hormones play a big role in it. There are simple hormone control techniques that are effective on most psittacines. We have an article about it at
http://littlefeatheredbuddies.com/info/ ... mones.html It takes about a week for the long nights treatment to have an effect on cockatiels. The time frame might not be exactly the same for ringnecks, but it's probably not too different.
It's possible that your birds will never be good buddies, but they will eventually form a flock bond with each other and won't want to be too far apart from each other.