Hi nelson48,
I am by no means an eyelash viper expert; however, I have researched their care, history and venom as much as possible since my fiance recently bought a baby male.
While many zoos do house them communally, the cages they use are massive, naturalistic enclosures, and the snakes are rarely found near each other in those enclosures. Exoterra does not make a cage that is really large enough to house several eyelashes. How large are yours? When they are babies, they do much better if housed in shoeboxes or small acrylic cages. They like to feel secure, and with a hot you want to be able to see where it is in the cage quickly.
In fact, the acrylic cages at Tarantulacages.com would be perfect housing for baby eyelashes. Their small to medium cages would house the viper for its first year to two years, depending on feeding rate, and then once it's an adult, it can be moved to the Exoterra.
TarantulaCages.com - Arboreal Cages (the 7"x 7" x 13" or 8" x 8" x 16" are good choices and cheap).
However, I would not house two adults in an Exoterra, and I would not house two babies in there either. You would lose track of the little guys easily in that cage, and that could create a dangerous situation for both you and the vipers- if you're rooting around with a hook trying to find them amongst various branches and plants. Simpler is better with hots, especially as these two are your first.
How big are your juveniles? My fiance's was born in December 2010, and is about 7" inches long. He's in this
Sterilite - 1874: Medium Nesting ShowOffs™, with a few fake plants and vines for him to perch on and many holes drilled for ventilation. It's very clean, very simple and you can spot the viper immediately before you open the door.
My personal advice is to keep them in small, separate cages until they are large enough for an Exoterra, then purchase another Exoterra and house them separately.