No. Being 'In Command' means you get the Leader's Bonus (+1 to Activation). It does not stack as (page 6) because you are on 'In Command' once. Your goal is to get all of your leaders within range of each other and to the troops by establishing a chain of command.
Skirmishers activate separately. "Skirmishers need not be in command. They always activate with their own Quality score." (page 6) "They always have Q3 and the Resolve Special Rule (so they activate on a 2 or better) and don't need to be in command." (page 14)
As they activate the same, they use the same mechanic. They can also cause a turnover.
Yes, they can move about however they want. BUT: "A pair of Skirmishers who take 1 loss immediately perform a Morale check: roll 3d6 against the survivor's Q. If he rolls more successes than failures, the surviving soldier receives a free Medium move that he may use to join a friendly Squad. Otherwise, he is removed from play." (page 14) SO if the survivor is not within an M of a squad when it tests, it is eliminated.
"Skirmisher" is a misnomer. They are the squad's sharpshooters, so it is better to think of a squad sending forth their best marksmen to raise a ruckus.
Corporals command the squad (page 3 and 7), but are not Leaders (page 6 and 7) and thus are a part of the squad's numbers. Rallying is not an action when the Corporal does it ("At any point in the owning player's turn (before or after the Squad activation), the Corporal may try to rally… page 7). Sgt O'reilly's is telling you to use the Corporal to rally, instead of using actions. See page 15: "The soldier remains Shaken until: the player spends one or more actions from the Squad to rally each individual Shaken soldier (one action rallies one soldier) or the Corporal tries to Rally him (see Corporals)." Actions have 100% chance to rally; Corporals have to take a Quality test and can cause a turnover.
Playtest Part One: link
Platest Intermission: link
Playtest Part Two: link
Q&A with the author (Sergio): link
More Q&A with the author (Sergio): link
Idea for smoothing out activations: link
Good gaming!
Dale