In a 180l tank you say your fish are hiding. To make them more visible plant it more densly (real or plastic). When an animal feels it can hide quickly at a moments notice you'll see it more where as in a bare tank they'll constantly hide.
A 3 ft tank makes it hard. Julies are predominantley down low and will be agressive if they breed.Unlikely to be a problem for your synos. Have you considered the calvus? Slow growing and less likely to breed but a fantastic fish all the same.
Fry have a high mortality rate in the wild less so in aquaria but if you have ctfish of any type then you're providing a very healthy high nutritional food source for them. Depending on the size of the tank and species you're keeping some should make it through. Invest in some liquifry food for them. Pour it in and the bits and particles will cling to the rock and substrate for them to feed.
If you can catch any and put them in a smaller tank then you'll be able to feed properly and ensure growth. The best way is sometimes to isolate the brooding female and then remove her back to the main tank when the fry are happy.
That looks really good. What is your tap water ph level? and has the lava rock affected it? Thie reason i ask is people would normally use ocean rock and the like to keep the ph higher for the rift lake cichlids.