MPPT for fixed DC use, or charging multiple independant batteries at once?
Since you're wanting to charge a variety of batteries, with potentially differing numbers charging at a given time, your "best bet" would be to connect several buck-boost converter based (or fluback converter based) chargers to the MPPT unit, and have each one charge a single battery.

With all PbH2SO4 chemistry batteries, you could easily enough build your own converters to output fixed current (or potentiometer-adjustable current) output @ 9V-14.2V (or whatever your battery mfgr recommends for float voltage) using any of a large # of available converter control ICs.