Littermates can work. And most of the horror stories come from those situations where people aren't aware of the pitfalls, and do nothing to help the two develop separately. You are aware now though

And there is plenty you can do to try to avoid it.
It will be a whole lot easier if you're more than one person though.
I guess what is tempting with two puppies of similar age is to do everything together. It seems easier, after all. So, they spend the days together, have each other for company at night. Play together, walk together, go to training class together, heck even go out to potty together... well, you get the picture. What is actually required is that they do most of those things
separately (especially the walking, training, and playing with you parts). You can start to see why it's easier to be at least two people
If you're quite fastidious about making sure that your pups have significant time apart, and each with plenty of one-on-one time with a person every single day, then you should manage to avoid the worst of the problems. I would expect you to need to be vigilent about this until they're at least a year old, probably longer. Well, certainly longer in terms of having
some time apart regularly. But at least that long in terms of significant periods apart daily. What you're aiming for is to create two distinct independent individuals, capable of surviving perfectly well without the other. And to acomplish that, they need to be apart for long enough, often enough, and in important/stressful enough situations to be unable to rely on the other for support/decision making.