The T&Cs state:
3. LICENSE GRANT
Simplify3D hereby grants to You a non-exclusive, non-transferable limited license to install and utilize the Software on a concurrent user basis for the Term. You may install the software on multiple computers that You own equal to the number of User Seats (stated earlier in agreement as 2) purchased by You. You are expressly prohibited from sublicensing, selling, renting, leasing, acting as a service bureau for the production of instructions or intermediate output of the Software (but not for the production of physical end products derived from the Software) or otherwise distributing the Software or making any use prohibited by law.
To me, what you propose to do falls within the above license conditions. There's no mention in the license about there being any restrictions on the number of multiple execution of the software on the individual "User Seats"....and my understanding of a "user seat" is a single instance of an operating system being used by a single user.
But there again, I'm no lawyer!!
As far as whether its physically possible to have two printers "connected" to two instances of the software running on the same machine....I've no idea. I'm currently using Windows 10.....and I can't even connect to one printer!!!