Based on the screenshot of the Skype chat you showed, it seems that "無力P ミュージシャン" is insistent on making sure that only Squall's name appear in the majority of the credits, since he only "made a basic participation how do performance of an instrument". Yet, on MuryokuP's twitter, niconico channel, and website, he/she has no qualms with stating straight out that he/she is the composer. There's also no mention of any collaborations or group affiliations anywhere.
Likewise, with Makai-Symphony, he's got a website, a blog, twitter, soundcloud that all lists him as the sole composer of the music in question. Again, there are no mentions of any collaborations. Furthermore, he is distributing the musical pieces under the creative license that allows free use for everyone. If your composer is the person who wrote these pieces, then wouldn't there also be a problem to the claim that the game is using a customized and original soundtrack when a number of its pieces are distributed under creative licensing?
Since I am planning on using Makai-Symphony's pieces for my project, I would love to get to the bottom of this and learn who to credit.