Welcome to the forums. Couple a cuties ya got there. Nice work getting an open mouth shot already too.

In my experience, when I've gotten a snake from a store or adoption and the snake seemed underfed and hungry it would take multiple food items for the 2nd and/or 3rd feedings then be fine with one food item afterward.

However! The little guy you have there could be younger and just weigh less for now. Either way, it sounds like what you have done just by upping the prey size sounds good. :-)