PWM solar charge controller MOSFET
I've seen this MOSFET configuration in a surge stopper circuit with an ideal diode (e.g. LTC4364).  One MOSFET clamps the voltage if it goes above a certain level, while the other prevents reverse current with a smaller voltage drop (and thus less power dissipation) than a diode.
It's not just the MOSFETs that determine the rating of a power converter such as this.  Protection and control circuitry, the current sensor, and internal wiring are designed and rated up to a specific power level.  Simply replacing the MOSFETs with beefier ones will not achieve a higher-current PWM controller, and could easily compromise safety.  Just buy/acquire a different one.