Hello, let me answer your questions one at a a time.
You do not need to own Charlotte, installing the trial will install the jetways, that should solve your issue. We had to include the Charlotte jetways as they were the only ones that had the correct height for the bridges.
Note: There is a GSX bug with the Charlotte jetways that causes them not to work, here is the fix.
There shouldn’t be any high-res or standard-res textures. We include one file that covers the entire ground poly, and all other files should be deleted or disabled. All of that is highlighted and on the installation page. It sounds like there are other ground files that are causing the issue.
Hope this helps!