I’ve had my two dogs for around two years and just found out about litter mate syndrome, I got them when they were both 9 weeks old. How bad is it? I JUST found out about litter mate syndrome like 15 minutes ago

I’m worried about this now since they have some of the signs like always staying together and on walks they can be more fearful/aggresive(just growing but they never bite) and they aren’t really separated that much, they share a kennel. How bad is this and what should I do?