Replicating from master to slaves and from slaves to master
What you are looking for is multi-master replication.  Multi-master replication has a large number of potential problems and consequently the best anything can offer is a toolkit rather than a guaranteed solution (imagine two concurrent updates on the same row on different servers).

Bucardo will do multi-master replication for two servers, but not three.  You could probably play some fun tricks with Slony and table partitions but this ends up getting complex and is definitely expert territory.

My recommendation is avoid multi-master replication if at all possible.  It is mathematically impossible to make it just work all the time without making it more failure prone than a single system would be.  Try hard to design so that you don't need it.

If you do need it, please look at getting some professional help whether it is a second set of eyes or a consultant (who can also get another consultant to review the design).  There is so much that can go wrong here that you really want additional eyes on the problem.