I posted this question everywhere I thought may possibly lead to clues or answers. I am pleased to say, like you suggested, I posed the question to the Muscogee/Creek Culture and History Facebook page and received the following two responses. I am happy with the insight.
Barb Alan Atkinson —- Old traditional names is a fascinating subject. Unfortunately, it seems not a lot is known on the subject anymore. I have been told that sometimes these names are just that, names. They have no other meaning, just a name that sounds good. Sometimes, the names are a common Mvskoke word like the "Mikko" in your question. "Mikko" is 'Mekko' (meek-ko) which means king/chief. It's a pretty common name. The rest is open to supposition, however. A common old traditional name is often phonetically spelled as 'Emarthla' or 'Emarthlee', etc... I've been told that it refers to a spirit who wanders, but I have not verified that. My best guess (and it is a guess) is that "Talmarthe/Tahnarthe/Tulmarthla" is a contraction of that name and 'Tvlwv', which means 'town. In which case, it likely would mean 'a spirit who roams a town'. The Mvskoke spelling would be 'Tvlmare' and be pronounced tull-mah-thlee. "SE-he-thi-ka/Sa-ge-tha/Se-ge-thla" would likely be spelled as 'Sekerv' or 'Sekerrv' in Mvskoke (pronounced see-gee-thluh). 'Kerrv' refers to one who is learning, like an apprentice or disciple. The prefix of "Se" generally means 'with'. So my best guess is that 'Sekerrv' is 'one who is learning from someone'. Again, all of this is supposition and my best guess. Don't take it as gospel. Continue to ask others and compare the responses you get. I wish there was more in depth analysis of the old traditional names. A lot of that information has slipped away over time.
Mary Conley Coffee —- Our GGG grandfather was Concharte Emarthlee. We were told by our cousin , Keeper, Concharte meant going back to the red ground and Emarthlee was a warrior word so it was changed to Johnson on the Dawes.