Just to clarify the rules on movement. These are off the top of my head but I think they are accurate.
You can always move through an ally's space. With the following caveats:
-You can't end your turn in an ally's space.
-If the ally is within one size category of you you will be considered to be squeezing while you are in that ally's space. So attacks on you have adv and you have disadv on attacks and dex saves and the occupied space is considered difficult terrain.
So this means people can move up in Ezraen's space attack w disadvantage and then back up (and provoke an OA that has adv) but she only has one reaction....for the record, I use this tactic with monsters a lot. Use one to provoke your reaction then follow on with others.
Bertram's nimble trait negates most of that...except he still can't end his turn there.
At least that is my understanding of the rules.
Can someone vault themselves over you and Topsy? Yes...that is where our cinematic rule applies. Acrobatics vs athletics/acrobatics. Success means you make it. Falure means you fail and provoke an OA. Failure by 5 or more means you fall prone and provoke an OA. Sound good?