There was a time when our kids, my sister and my brother's kids didn't get along, one was one and a half, the other was a year and the next six months. The 1.5 yr was always hitting the younger ones. Now they get along much better. Do you think it's because they are now used to each now? The eldest one has also started school.

I am sure that school has calmed the first one, that's one of the first disciplines they learn, it's pretty normal to have that kind of rivalry, it's good that they are actually getting along now, it may change again.

I think it's just maturity. Being so close in age, when they were young, it was either ignore each other or hit each other, LOL. I hope they continue to be good friends and get even closer.

My kids are a bit older now but they always love to see their cousins. Unfortunately, the cousins live pretty far away so I think that's why they all get along so well.
Honestly, if we saw them all the time I'm sure there would be some disagreements as they all have pretty strong personalities.