How many GAS IT bottles can I connect together?
There is technically no limit to the number of gas bottles you can connect together from 1 fill point so they all fill together, In fact you can also connect more than 1 fill point to a GAS IT bottle system so you could have 2 fill points to 1 or more bottles so you can fill from opposite sides of a vehicle for example
All you need to do is make sure you have the right number of connection tees and hoses to connect them together.
It's also with noting that you can mix and match any size of GAS IT bottle together as 1 fill system, so you can have a 6kg and an 11kg for example.