Quite correct with O's and Africans, each requiring different water. There are a lot of compatible Oscar tankmates, but huge space and volume are needed. Assuming you follow advice and separate the Africans, you still need within 6 months a 6ft tank of 150+ gals for 2 O's and a pleco. Oscars, with proper care will easily surpass 14ins and some plecs can easily attain 18+. They all grow quickly.