Julies do not get that large. They would most likely get eaten.
The Ph is not what really matters, consistency is key when dealing with mixing fish. The real issue is mixing sizes and levels of aggression which can generally be a crap shoot at best.
The only aggressive fish in my tank is the firemouth and hes all bark no bite... I just put a jewel cichlid in and its doing very well. so it will either be another jewel unless anyone has any other suggestions
just go with the lone jewel, which can become the most aggressive fish in your tank, so adding a pair might not be a good idea, as they can cause some damage paired up