How do you know BT Tattletail and EBT Tattletail are boys?
Of course, they are robots. Robotic Toys. (And just like in FNaF, the robots do NOT have genders.. unless your talking about the kids in them. But still, the robots themselves don't have any type of gender.)
Did "Waygetter" (aka ben espito or something) confirm they are boys? Or something?
The release trailer refers to BTT as "he" and since the Kaleidoscope campaign involves a slightly different Tattletail, it makes sense to refer to EBTT as "he" too. I think the game uses "he" for both of them at points. I'm sure that means Ben Esposito confirmed it.