When Paul was working on that crane in container city #2 I couldn't help but ask myself if 2 or 3 engineers couldn't repair the crane at the same time allowing teams that choose to have more then one engineer around to blow through certain objectives blazing fast.

No, but you could cover that person and get XP for doing it.

I think it depends on the objective really.

Where'd you hear that covering someone who is doing an objective gets you part of that XP?

You could do it in their previous games, but obviously it does not work for Destroy objectives in Brink but it's still a possibility for it to work on Construct / Hack objectives.

I read it somewhere. Defending objectives gets you XP. Its not anywhere in particular, I should say. Standing near it gets you XP. It pops ups the more time you simply stand there.

In previous SD games, the more engineers that repaired/built something, the faster it got done. This was the same for hacking with Spec-ops (Operatives) as well. Everyone who participated got xp as well, from what I remember.

Guarding/escort the robot in Container City does work with mutliple people, I believe. Also if the Resitance damage it, several Engineers can repair it simultaneously.

But hacking the crane with several people seems like a hard task, since it has only that one small cabin.

You can't stop two people picking the same objectives all the time...

Of course you can't. But if one of them is hacking something, the other simply can't help him other than shooting incoming enemies.

What does the XP percentage split appear to be when one is on the objective and the other is defending?

The one doing the actual task gets the objective-xp. The one defending gets like 10XP per tick.

What's to keep people from racing each other to objectives and holding grudges?

There are worse things than having a pair of players trying to get to the objective as fast as possible.

This is true. Hopefully it will always be a somewhat fair race.

doubt it, seems like a light would have a huge advantage over a heavy in completing an objective first.

Heavy would have a huge advantage over the light in finishing the objective, which is when the XP is given.

In terms of higher HP or does the heavy complete objectives faster?

The enemy is always going to be trying to stop the enemy from finishing the objectives. In the first container city footage, there are barely any shots fired at the crane cockpit because the enemies are all on easy. In the more recent container city footage, you watch a soldier get mowed down as he plants the bomb. I expect the latter to be pretty common in normal play.

Lights will have an easier time getting to the objectives, but if a heavy manages to get there, the opposing team will have a hard time downing him before he finishes.

On a side note, there are skills that speed up completion time for planting, defusing, hacking, and probably other stuff.

You think some bullets hitting you can interrupt certain actions? Wouldn't that be more realistic? I didn't see that with the bomb plant video. But maybe it slows you down?

Realistic? Yes. Needed? Absolutely not. You're already vulnerable when you're doing an objective because you're not holding your gun. On top of that, people will prioritize an engineer near a construction objective.
I think you can construct/repair together. In their previous games you could plant more bombs near destroyable objectives, but I don't think this will be the case in Brink (Fixed animation, like the door in container city)
While standing near objectives, near teammates who complete objectives or just near teammates, you'll receive a bonus multiplier for teamwork.

Heavies won't be able to rush objectives like lights can, lights however are easier to kill while they are standing still completing the objective. Heavies are more suitable to help teammates directly (giving ammo, buffs, health) because they have more ability pips than lights. They are needed to give objective completers covering fire.

Also , you're able to chose the same mission as someone else on the mission wheel.

Yes, but in the interviews (and container city footage I think) Paul Wedgewood stated that the A.I. that kind of leads you along will prioritize your class and where you are on the battlefield. So maybe not everyone will be given the same objective despite being the same class.

You are shown all of the objectives you can do at the moment, with the closest ones being prioritized, but there are no hidden ones. You can even see what missions the other classes can do, with a mission even being offered to change classes to do the important ones, if there are none of the required class on your team.