Checked that at https://en.wikipedia.org/wiki/Seiko, https://en.wikipedia.org/wiki/Seiko_Group and https://en.wikipedia.org/wiki/Epson, but got away confused.

https://en.wikipedia.org/wiki/Seiko_Group seems to have the best succinct description (but reading the others, it does leave out info):

“Seiko Group (セイコー・グループ, Seikō Gurūpu) is a corporate group composed of Seiko Group Corporation and its subsidiaries and affiliates. It used to be recognized as a corporate group consisting of three core companies Seiko Holdings Corp. (Seiko; f/k/a K. Hattori & Co., Hattori Seiko), Seiko Instruments Inc. (SII; f/k/a Daini Seikosha, Seiko Instruments & Electronics), and Seiko Epson Corp (Epson; f/k/a Suwa Seikosha). The three companies were linked by a common thread of timepiece technology. Although Epson still develops and manufactures wristwatches for the Seiko Group, Epson and its subsidiaries are not considered part of the group”