Bigfoots run either 2.5 or 3 feet. Just depends on specifics for the role. With a 6' height minimum, you'll most likely see 9' and taller.
I personally have no clue what's happening, but when hearing a current park IP will be used, along with bigfoots...I thought Deatheaters. I'd assume they're using the stilts to carry additional weight, which could mean stilt walkers puppeteering large puppets.
Again, this is entirely personal speculation.