I have a 10g tank and 4 Cichlids. What would recommend for the maximum care? food, decor, number of fish, etc?

I have recently obtained 4 Cichlids from my boyfriend's buddy who has a helluva lot of em. There are 2 males and 2 females. How many would I be able to keep in all in a 10g tank? Also, what decorations can be used; can I use any household items? His buddy would often feed them goldfish as a treat, is this healthy for them or is there something else I can substitute? My tank right now has a piece of petrified wood in the back, pebels and small rocks instead of gravel, a bubbling gargoyle, a plant in the back corners and a plant in the center. All 3 plastic. Also the largest male chases the smaller male until he hides behind the filter and won't let him go anywhere else. The larger male also seems to be semi aggressive to the other female. They are all inbred.