How can I connect more than device on the same Isolation transformer?
You can power multiple devices from the same isolation transformer.  However, in some cases this makes the setup less safe.

Whatever is powered from the isolation transformer requires two connections to some other object (like you) for current to flow thru that object.  Equipment that is powered from a unisolated source can cause shocks with only one other connection.  That is because one connection has already been made to ground.

The more equipment you power from the same isolation transformer, the more chances of one accidental connection to the rest of the world, thereby making everything else less safe.  This is what the paragraph you quoted seems to be referring to.

However, there are also safety advantages to powering more equipment from the same isolation transformer.  You are still more protected by two connections being required before shock.  If the multiple pieces of equipment need to be directly connected together anyway, then you must power them from the same isolation transformer if you want there to be any isolation.