How do I get to complete the two star challenges? I keep going to do them online with people, but every time it seems to be the one star one, and I don't get the rewards! Is there a way that I can turn on the two star challenge or something? I'm trying to do the Be More Objective 2 star, but it keeps giving me the one star one, and I can always finish that one in like 1 minute because its so easy.

You can't complete any of the star challenges online with other players. You have to do them solo in order to complete them and unlock the attached rewards.
But on that note I really hope they make it so players can complete the challenges with online co-op. Cause the three star combat challenges are a pain when on your own.

Okay, how about the Be More Objective 2 Star is impossible then! The hack box objective is way too hard. Because the box is right next to the enemy spawn, and my team doesn't do anything!

on the be more objective hack part try a gun with a huge clip be patient and kill them all and place the box on then move to the other side where the CP is u can climb up above it sit there and most likely they wont disarm it keep trying if u fail took me like 20 trys before i found that spot.

I went Heavy and took the Hjammerdeim, then swapped it for the Chiznor when I was going for the hack.

Gun down everyone, place the box, and go around the corner. There's a small alcove spot you can crouch in where you're still close enough to keep the hack going, but you're out of sight, and your teammates will usually be enough of a distraction to let you get the objective done.

Also, try with a lower level character - the enemies are WAY less dangerous at lower levels.