Homura's witch's labyrinth was inside of her soul gem, and didn't actually occupy and physical space. How, then, were all of the magical girls and everybody else brought into her soul gem? How did everybody that was shown in her labyrinth get into it in the first place? Wouldn't they have to physically go there and get into her soul gem somehow? Were they just teleported there by Homura since she "willed them to be there"?
It's implied that Homura wished for them
When Homura questions how people came to be trapped inside the barrier, Kyubey explains they made an adjustment that allowed things to be "invited" inside. Images of the familiars appearing in the real world behind Mami, Kyoko, Hitomi, and Kyosuke are shown, implying they abducted the victims and pulled them into the barrier. Kyubey explains that the people trapped in Homura's barrier are people that Homura subconsciously wished for. Futhermore her barrier could also invite the Law of Cycles itself, which would allow the incubators to observe what causes the disappearance of magical girls when they run out of magic.
What i do not understand however is why Episode 4 is linked. I suspect that because in Episode 4 we see Hitomi being controlled with a Witch's Kiss to where the Witch Elly and her Labyrinth was this could imply that Homura as a Witch wished for others to be with her by sending "invites" in the form of Witch Kisses (to put them in a tranced state similar to Hitomi and Elly's other victims) and her Familiars tracked them down while the Incubators allowed them to enter Homura's Barrier.
The Isolation Field is meant to isolate Homura's Soul Gem from external influences but it still allows her to call out to the Law of Cycles which is what the Incubators were after, seeing what happens to a Soul Gem in a controlled environment (and they only learned about the Law of Cycles after confirming the existence of Witches by isolating a Soul Gem turning black) so with that said i do not not how the Familiars were getting out but it's possible the Incubators were allowing only them to leave