To keep the loyalty will be very hard, especially to the members of the group without strong connections simply because temptations will be many.
It is visible from the experience in totalitarian regimes where everything is set up that even small things (like extra food) simply means a lot, so temptation is big.

When SHTF, no matter how many people with good skills you have in group, if you do not have something that can “connect” you all together, then you are just bunch of folks, happen to be together by luck or chance. And that group will fall apart or even worse.

That connection can be blood or good friendship, but still there need to be lot of time spent together, to the group to be very good.
Of course there s exceptions, so couple of guys who just meet each other can do very good in some chaotic situations, but it is rare, and if SHTF scenario last longer, there s more chance for falling apart.