First , In my opinion, your Oscar will eat those barbs and SAE. If he dont the texas might.
How long has the tank been up?
What is your maintenance schedule? 25% water change every week?
You should with the pooper plecoes, and the messy Oscar get a Nitrate test.
Your Algae could be from too high of Nitrates in the water. Sometimes the algae can develop from Phosphates in your tap water as well. If the algae is the black short hair kind, then this would be what it is comming from.(Nitrates or/and phosphates)
Make sure you keep you weekly water changes up, Vaccum the gravel real good (Are these real plants??)If your nitrates are high, you will have to do a few extra water changes at first to get them down.
I feel the mix of fish is not what you want(in the long run) as well, but that is up to you.
Dont get Otto cats with those types of Cichlids.
Your SAE(you positive they are true SAE?)probebly enjoy eatting the other food more , that your pleco and others leave behind.(that is just a guess)