The secret behind the whole thing is that it started as a joke. Someone came onto one of the facebook language group and tried to tell us his language was the mother of language. So I said "Atlantean is the mother of language". But that then gave me a good idea for a conlang.
So the main idea is that Erd (the world where Atlaans is spoken) is an alternate version of Earth where Atlantis is real and had a large effect on the world, large enough that all languages come from some form of Atlantean. So "Atlantean is the mother of language" is technically true on Erd.
My idea is that Harbour Atlantean and Dairy Atlantean are Erd's versions of the Germanic and Slavic families. So when I make a language that is descended from Middle Atlantean (it's kind of like the Proto Indo European of the world, since most language are derived from that form of Atlantean, and it parallels how many European languages come from Proto Indo European), I try to make it resemble a language that we on Earth know.
So obviously Atlaans looks like Dutch and German, and obviously they were the inspiration when I created Atlaans, but on Erd it has a completely different origin. I really like to mix things together. Who knows what German would have looked like without the sound shifts that separated it from Dutch. What would English sound like if it weren't for the Norman invasions.
So Atlaans has some English features (and older elements of English, like /o:/) as well as some Swedish features. And Tohanian uses modified English pronunciation. It's all to make a plausible world that is kind of like a distorted version of our world. Like looking at our languages through a fun house mirror