I’m a Child Passenger Safety Technician (aka car seat tech), mom of 3, 2018 Expy MAX owner and former 2011 Pilot owner.
With the RodiFix and 2 very slim backless boosters, you could fit all 3 in the 3rd row. The backless boosters would need to be extremely slim. If the oldest 2 are both at least 50 lb, the Graco RightGuide is your best option for super slim backless boosters back there. If one or both are 40-49 lb, the Bubblebum is probably your only workable option. The Mifold would technically work on paper but has some fit and usage issues that always make me hesitant to recommend it. You’d want to put the RodiFix on the passenger side and the 2 slim backless boosters center and driver side.
The 2nd row is quite easy for 3-across. The RodiFix is also one of the few high back boosters that works well 2nd row center if you ever need to use it there.