Hello Koepel,
Thank you for your reply!!! Very helpful stuff.
If by chance you hear of Aliens attacking next week, then you'll know it was cause I used the all Slave method... 
I think the reason my double Slave method was working was because I was using interrupts between the two and it was impossible to talk over each other.
But I will follow your polling recommendation instead.
Thank you for your thoughts, help and advice! Have a great weekend!