What happens if a particular player is said to skip his/her combat phase in a Two-Headed Giant game (for instance, if someone had cast Moment of Silence)?
Is the whole team unable to attack, or is only that particular player unable to?
The whole team is affected, according to rule 805.8 as of the 28 August 2016 revision of the comprehensive rules:
805.8. If an effect gives a player an extra turn or adds a phase or step to that player’s turn, that player’s team takes the extra turn, phase, or step. If an effect causes a player to skip a step, phase, or turn, that player’s team does so. If a single effect causes more than one player on the same team to add or skip the same step, phase, or turn, that team adds or skips only that step, phase, or turn. If an effect causes a player to control another player, the controller of that effect controls the affected player’s team.