Forseen was a compromise name after he kept bouncing weird names off of me that I refused to let him keep (like, Instanculus? Uh, no, that sounds like a type of cloud). Original placeholder name was Aiden, which changed to Ayden later cuz I forget why. Anyways, now we've got Forseen. Which literally sounds like forcing. Maybe that's where he got it from, I dunno.
Muse's name came with her form. You'll find I panic when I've got a tulpa with no body, and I just grab whatever thing is present at the time as the form (did this with both my accidental tulpas). At that point in time, my mum was trying to order a ball-jointed doll for my cousin from MuseDoll, so her form became one of the doll models in the shop and her name came from the name of the website, Muse. I've let her change t, but she's kept them all cuz she likes them.
Alix is an alternative spelling of Alex that she wanted. As for where Alex came from, it was the name she said to refer to her as when I first talked to her. Found out later she was an old servitor friend I made when I was like nine who was named Alex. She turned into a tulpa when I put Forseen and Muse's sentience and personalities in her.