OP, the list of approved trailer rental vendors at Fort Wilderness can be found at this link (click the "Read More" link on the RV Rentals section if they are not already showing in that section):
https://disneyworld.disney.go.com/resorts/campsites-at-fort-wilderness-resort/services-amenities/
I suggest you ask any follow-up questions on the DIS Camping Board
https://www.disboards.com/forums/camping-at-disney-world.24/ lots of DISsers over there have rented trailers.
Bigger units will sleep up to 10 but that generally means using all available sleeping conveyances such as sleeper sofas, dinettes that fold down, etc. in addition to bunk beds and regular beds. You have to decide if it's worth setting them up every night and breaking them down every morning. People in tents are quite common and I would not be concerned about gators in the campground. There are canals around the Fort and they do contain gators (what body of water in Florida doesn't) but the gators are trapped and removed if they are of a certain size. Given the recent sad events, Disney is probably even more vigilant about doing so now. I let my kids sleep in tents on my site.
Bama Ed