Why that's a Tiki 38! I'm in the process of finishing mine, where are you based?
As for the charging, you can't really charge Li batteries from the outboard without some kind of external charge regulator. You run the risk of damaging the batteries and/or the alternator. The 10A output is at max RPM and you're not likely to see more than 5 or 6A at normal running speeds, though you can run them both at the same time of course. That will probably replace the starting drain but is not really practical for general charging.
The other, more critical thing is that the charge profile is not safe for the batteries. You can find some details here:
https://marinehowto.com/lifepo4-batteries-on-boats/
and a lot more information on safe design parameters here:
http://nordkyndesign.com/category/marine-engineering/electrical/lithium-battery-systems/
It's not safe (for the Li batteries) to simply plug them in to replace lead acid. The charging system will need to be set up for the new batteries. Given the surface area you have available and the low cost of panels, more solar is likely the most efficient and effective solution, particularly if your current solar controllers have some excess capacity available.