According to the Comprehensive Rules:
711.1. Two cards ([[[Mindslaver]]] and [[[Sorin Markov]]]) allow a player's turn to be controlled by another player. This effect applies to the next turn that the affected player actually takes. The entire turn is controlled; the effect doesn't end until the beginning of the next turn.
711.4. The controller of another player's turn makes all choices and decisions that player is allowed to make or is told to make during that turn by the rules or by any objects. This includes choices and decisions about what to play, and choices and decisions called for by spells and abilities.
805.1. Some multiplayer games between teams use the shared team turns option. It's always used in the Two-Headed Giant variant (see rule 810) and the Archenemy casual variant (see rule 811). It can be used only if the members of each team are sitting in adjacent seats.
805.4. Each team takes turns rather than each player.
810.2. The Two-Headed Giant variant uses the shared team turns option. (See rule 805.)
Unfortunately, there's no explicit rule for the interaction between rules 711 and 805, but it can be reasoned as follows:
- The team shares a single turn.
- Another player is controlling that turn.
- All of the effects in rule 711 state that if the turn is controlled, then it affects any player whose turn it is.
- Therefore, [[[Sorin Markov]]] and [[[Mindslaver]]] let you make all decisions for all members of the team, not just the targeted player.
Note also that Archenemy uses shared turns, which makes that effect extra appealing for a certain villain.