Don't see the relationship between Marriott and Sheraton TSs.
There are now two connections:
1) the Marriott International hotel company acquired Sheraton and the other Starwood hotel brands (Westin, St Regis, etc) a couple of years ago. This includes ownership of the Sheraton Vacation Club brand (as well as the Westin Vacation Club brand). Marriott International also obviously owns the Marriott Vacation Club brand. You can see all of the hotel systems Marriott owns in the list of logos at the bottom of the page at
www.marriott.com
2) Marriott Vacations Worldwide (the separate company which owns and operates Marriott Vacation Club) announced in late April that they are acquiring ILG (which owns and operates Sheraton Vacation Club, Westin Vacation Club, and the VSN network). If that merger closes as expected by September 30, a Marriott-afilliated company will also own and control the Sheraton and Westin timeshare programs.
So, to summarize - the Marriott International, Inc. hotel company owns the Marriott Vacation Club, Sheraton Vacation Club, and Westin Vacation Club branding rights; and after September 30 (if all goes according to plan), Marriott Vacations Worldwide, Inc. will own, operate, and manage the Marriott Vacation Club, Sheraton Vacation Club, and Westin Vacation Club programs and sales.