north has two tunnels, with same rihgtsubnet and different leftsubnet.
One goes to east and the other to west.

Yes this test is special, configure same subnet behind east and the west!

Since both tunnels have the same rightsubnet, pluto refuse to add the
second tunnel.

The limitiation is from the KLIPS days, where a route meant destination + next hop.
Now a days source is also part of route, and more attributes with routing policy.