Chaining sshuttle commands over two hops
Use ProxyCommand like for every other multi-hop setup. Create a file ~/.ssh/config with
Host B
Hostname 192.168.1.1
User root
Host C
Hostname 192.168.2.1
User root
ProxyCommand ssh -W %h:%p B
Then just connect using sshuttle:
sshuttle -r C -v 192.168.3.0/24 &