Then there is links to two FM Synthesizers that have been talked about before here at Musical Android-
SynprezFm is in my opinion one of the better synthesizers you can get for Android-
Don't have a sequencer though but there is arpeggiators that you can use and it's possible to divide it in into two synthesizers at the same time.
(and using two arpeggiators at the same time).
Then there is the simpler one but also a nice one- Common FM Synthesizer.
Lastly there is a link to FM Tutorial- which is an application that will help you to calculate your sound when you are using FM Synthesis.
Common FM Synthesizer