I'd stay where you are for now but see family more often if possible.
If you move there, there's no going back really due to the disparity in CoL. It's different when you're young, single, childfree and starting out. You don't mind so much being a bit poor then.
Once you're older and have got used to a certain standard of living you don't want to let it go. So if you couldn't find work it wouldn't be so easy to just come back down South, but you could change your mind and move North at any time.
It's harder to make friends when you're older too, at the moment you've got some, I wouldn't give them up in a hurry.
Maybe further down the line when you and your friends have possibly lost touch as DC grow older or if one of you was facing redundancy etc, you'd have less to lose by moving back North. Or if the idea crystallises in your mind as something you definitely want to do, perhaps to help parents out in old age or because you've become jaded by the South.
But for a maybe? No, I wouldn't. You'll get there and find the grass is no greener, that you've swapped one set of problems for another set.
Maybe your cousins wouldn't be available so much as you'd like, if you moved back North. Maybe the DC would grow apart and naturally not want to spend so much time together. Maybe you'd feel pressured to provide elderly care and not want to.
You've got a life that's working out well at the moment and no real idea exactly what you'd be swapping it for, only a rose-tinted vision of DC playing happy families with cousins. That's not enough to base a life altering decision on.
You have annual leave, so do your family, visit each other more often and see how you feel in a few years.