My Girlfriend and I have for the first time started playing the Thieves Guild DLC, and we were under the assumption that performing the Thieves Guild daily Heist quests would be easier to achieve when playing together. The heist itself is not a solo instance, and allows you to bring other people in your group. While we were attempting "Heist: Underground Sepulcher" specifically, you must loot three randomly located chests, and one "Treasure Chest" before the timer runs out to achieve the highest rewards; however when one member of the group loots one of the random chests, it does not count for the other group member unless the two are standing next to each other.
This means (as I understand it) if you are to perform the heists with your friend, they would have to follow you around like a duckling throughout the entire quest; or perhaps the group split up and hopefully all members finish the heist in time, without any of them getting caught; seeing as if one person gets caught it reduces the timer for everyone in the group
Either scenario, it evidently makes the Thieves Guild Heists even more difficult when you opt to play with a friend or two.
I'm uncertain if this was an intentional design choice, or perhaps this was something that had been overlooked, seeing as i'm most likely in the minority, in regards to wanting to perform Heists with friends and not alone.
If you are truly intended to perform these heists solo, then I would perhaps suggest making the Heist instance a "Solo Instance", where group members can't enter and make it even more difficult for you to complete before the timer runs out. If on the other hand, it was the intention to have people be able to perform Thieves Guild Heists together as a group, then perhaps allow it so when one person loots a chest, it counts for the other member/s in their quest log.
I would really enjoy to hear some feedback and your own personal opinions on this subject.