Different 4 handed siteswaps are compatible, meaning that juggler 1 can do a different pattern than juggler 2 – that´s especially great for juggling groups of mixed skills – better jugglers can pass a difficult pattern against an easy one.
Christian Kästner compiled an online, searchable list of compatible 4 handed siteswaps.
In this list, the numbers mean:
2 = zip (very fast self without spin)
4 = hold or flip
5 = zap (fast, half-spun pass)
6 = single self
7 = single pass
8 = heff (double spun column self)
9 = double pass
a = 10 = triple self