I would not advise this (the crushed coral) with the present mix of fish and current chemistry in the tank.
I have used a mix of crushed coral and aragonite (which adds both calcium and magnesium for a better balance) and found it drives the pH up very high and very fast, and with only about half a cup in a 115g tank. The GH went up by 3 dGH max, but the pH went from 5 up to 7.2 which is significant.
Seachem Equilibrium raises only the GH with no effect on pH, and as it is measured; 1 tablespoon in 20 gallons raises GH by 3 degrees, depending upon the initial chemistry. The buffering products I have not used as I had no reason, wanting a low pH.
You have soft water fish and medium hard water fish. The livebearers need medium hard to hard water, and a pH above 7. Molly in particular will be healthier in harder water, with a pH close to 8 (high 7's). But this is not the best for neons and rasbora. While it is true that these species can somewhat manage/adjust to harder water, they still will be healthier in soft, slightly acidic. They will generally live longer, and have less health issues.
I personally do not advocate mixing livebearers with soft water fish, simply because one of them is going to have to live outside the preferred range and this does affect the fish.