Tiaral

How will our characters look in global battles?

In what sense? They add their converted stats to the squad's stats and are considered "last" in the order of damage received. Except for speed. It always decreases to the lowest value.

In that case, will the bonuses from the character's attributes (except for commander skills) not play a role?

If you're talking about what I just wrote, then they will, but only for one squad.

Can player characters be added to squads as units?

They will be added as units, but additional bonuses will not apply to them.

What about quests? Are they exclusively defensive and offensive, or are there mixed options?

It depends on the quest. Using characters in squads is generally optional, although it undoubtedly increases the chances of victory, and the recruiters will simply need guest generals. Sometimes this can be part of a quest (for example, winning a large-scale battle to unlock access for the main group of characters to advance or to make the quest conditions easier) or a full-fledged campaign. Sometimes it may be enough to send one character on such a "quest," while others do something else, for example.

Added 1 minute ago

What about disabling shots?

No.