I have got a gap of 16 months between the first two and then it's a 3 year gap. Poor old Harry, the youngest gets so much crap now from the older ones it's not funny.
When the first two were younger, they were like two peas in a pod. When the 3rd came along, it was cool, but as they got older they fought heaps and still do

LOL, now I have a 10 year gap, but that's a different story altogether