Which strobe to use?

I just got two Sea&Sea strobes, a YS-02 and a YS-03. As I have not dived with them, I am wondering:
Which of the two is better to use underwater for (close up) macro shots with a housed Olympus TG-6 camera?
I feel I do not need to use both, just one, is that correct?

Thank you for your expert opinion. 

I would use both. 

The YS-02 lacks TTL, but can slave off the YS-03 which has TTL. 

You can also use the YS-02 in manual with the TG-6 which has a manual flash triggering option.  It depends on whether you want to use manual or TTL flash. 

I’ve never had much luck with TTL so I would choose the ys-02.