Precisely the weakness of duolingo. There are different usage styles of articles in English that one italian word cannot fully represent: I can speak with them, i can speak to them (which is not completely right), i can speak of them, i can speak about them, and -di loro- could mean almost any of this. You can also use "talk" here, instead of "speak" verb. We need a better natural language processor within Duolingo.
Are commas used in Italian the way they are used in English? The meaning changes when the commas are used: "I speak, above all, of them"--Clearly means I talk about them more than anything else. "I speak above all of them" without the commas to me means "my speech is somehow higher or better than theirs."
This phrase translates awkwardly to English, as we would not phrase the idea this way. It's contextual - just a part of an overall conversation and places the emphasis on THEM. So, whatever I'm saying at this moment, especially applies to THEM. I'm really talking about THEM. I particularly mean THEM. Whatever I just said may or may not apply to you or me, but it DEFINITELY applies to THEM. Soppratutto is an Italian word, so Im presuming learning it has a purpose and that its distinct from soppra tutto. It's okay to make mistakes.. It's all part of the learning process and helps cement the finer nuances of the language in our minds.