[RPG] Dealing with 2 Immature Players Who Detract from the Experiences of Others

I have read a number of threads here similar to but not the same as the problem my group and I are having (including this thread, this answer, this answer to a similar situation, and this question which addresses only 1 person).

I have a question related to dealing specifically with 2 problem players, and would like to explore avenues of resolution other than disbanding or kicking these players out of the group.

After joining a new group recently, I am finding more and more that two people in the group are surprisingly immature, a fact not helped by them both feeding off of each other's behaviour. While this is not necessarily a problem in and of itself (and in theory could actually lead to some fun interactions), it is unfortunately leading to some detrimental effects for the rest of the group (and the DM in particular). these effects include:

• Slowing the game down – When these two players get together, they tend to distract one another. This is especially frustrating when playing with a larger group (5 or 6 other players), since in talking to one another they miss what is happening, and we consistently spend time having to catch them up on what other players have done, the state of the battlefield, etc. While not a huge problem for me as a player (though certainly irritating), our DM is getting understandably frustrated having to repeat everything twice, since neither of these two players are paying attention. They also don't think ahead when its not their turns, and since they are both spellcasters, this frustrates us other players a great deal, as our turns often take under 30 seconds, while because of their distracting behaviour their turns frequently take upwards of 5 minutes each.
• Losing a sense of cohesion – Their two characters almost exclusively look out for each other, even to the detriment of the rest of the party. While this could make for an interesting dynamic in game, their behaviour is inconsistent, and they appear to show little loyalty to the order our group serves (around which our 2 month campaign has been based; loyalty to this order was the prerequisite for joining the group), our overarching mission, and more importantly the welfare of our group (eg last session they refused to heal our tank because they wanted to save their healing spells for "more important characters"). This is, unsurprisingly, leading to resentment both in and outside of the game.
• Ruining Immersion – A large draw for many of us to this group in particular is the role playing aspect of the game. However, the constant bickering and out-of-game discussions among these 2 players is constantly drawing us out of the game. Our DM has tried calling them out at the table for being distracting and taking away from the game, as well as speaking to them privately (though I was not present when this conversation took place). Regardless, the poor behaviour continues, and our DM appears to be at his wit's end.
• Poor Gameplay – Before anyone gets upset about me listing this, let me explain. The two players tend to make decisions against the advice of the rest of the group and the DM (which is fine – after all, we are roleplaying). HOWEVER, these decisions (unsurprisingly) often lead to a poor situation for them, to which they respond with resentment towards the group and the DM, consequently leading them to spend the rest of the night complaining about how boring the game is, and further distracting the group. For example, in our last session we were fighting a group of dragons. Rather than mounting their dragons and helping in the fight, both decided instead to head into town and get drunk, even after the rest of us, including the DM, advised against it. When they realized that the rest of us were having a great time slaying Shadow Dragons, they complained that they were stuck in a tavern in town essentially doing nothing, and began berating the DM for not allowing them to instantaneously join the battle. We are unsure of how to handle this behaviour, and their boredom undoubtedly contributes to the distracting behaviour that is frustrating the rest of the group.

Ultimately, the question boils down to this: How do we deal with 2 immature players who feed off of one another, and detract from the experiences of other players?

Although simply kicking them out or forming a new group is certainly an option, I figured sharing our predicament with the wonderful RPG community here may lead to some unexpected solutions which may help us actually resolve the problem.