Relaying changes to a slave from another master with Tungsten on MySQL
I don't have direct experience with a similar setup, but you probably need to set this option on the master services:

--log-slave-updates           Should slaves log updates to binlog [false]


By default, changes made by appliers are not written to the binlog. As Tungsten watches the binlog to detect changes, the master extractor will not see those changes made by appliers, unless you specify the options above.