I can't currently see the pic of your test results, but it sounds as though your pH is 7.4? If that's correct, you don't have a thing to worry about, at least regarding pH. Virtually any fish you are likely to choose will be fine at that level; some species from more acidic natural environments might be less likely to breed at 7.4 but should be otherwise healthy. Even those species will likely have been captive-bred for many generations and are already better adapted to the more alkaline water than their wild-caught ancestors.
I have water that is usually around pH 7.5 or so. I don't worry much about it, especially when dealing with small species in particular. Platies, tetras, barbs, etc. have natural lifespans too short for long-term chronic effects to show up, assuming that they ever will. Large cichlids, large catfish, etc. live much longer and so if you keep a fish that will live a long time and is also sensitive to higher pH then perhaps a problem might eventually develop.
So, yes, you can buy an RO unit which will produce soft, acidic water, and you can mix this with your hard alkaline water to create a more middle-of-the-road chemistry which is theoretically better for most fish...but IMHO all you are doing is wasting money, creating more work for yourself, and virtually guaranteeing that your tank will experience up and down swings in pH which will...again, IMHO...be far more deleterious to your fish than a stable 7.4 ever would be.
It ain't broke...so trying to fix it is...IMHO...just creating potential problems where none currently exist.
As an aside...I love Oscars. I think they are one of the most underrated fish in the hobby, in terms of beauty, personality and just about any other yardstick. But I don't keep them, because they are one of those long-lived species from low-pH water who may develop HITH erosion issues when kept long-term in hard, high-bacteria-count, nitrate-accumulated aquarium water. The point being that you just have to resist the temptation to keep species that aren't well suited to the conditions you can provide. Luckily, in your case, just about anything you are likely to put into a community of small fish will do just fine in your water...no pH-juggling or RO-ing required.