I have 2 trailers I want to join together. I have inherited 4 children and I need the space.
Google for "join two single wide mobile homes together". You can find what other people have done.
It looks like one parks them a foot or so apart then builds 'hallways' between for access.It doesn't sound easy. Won't you need another complete hookup for water and waste?
If you are relatively well versed in construction techniques, you will be able to join the trailers, your success level will be determined by just now cohesively you want to graft the two together. Why join them at all, leave them separate, structurally sound and water tight. If you want a common space between them, add a deck or enclose a room, but leave the trailers themselves intact.
This comes to mind:
Reminds me of the time when I was a kid, our neighbor came over to borrow a pair of tin snips.
Dad: What do you need them for?
Neighbor: I'm adding on to my trailer house.
Dad: Let me get you a can opener...
Moshe Safdie did the same thing when he designed housing for the '67 Montreal Olympics.
Trailers can be joined but I would only recommend it to someone already well-versed with construction and trailers already. You're going to find that sealing the roofs together well is near-impossible unless you do a full roof-over. You may run afoul of building codes which probably won't allow this since modifying the trailer structure loses the manufacturer's certification. To do it well is going to take a large time investment and isn't really worth the effort involved.
You'd do better to trade the old ones in on a double-wide. I'm well-versed with and have much experience with trailers and I would never attempt this even of someone gave them to me- it just ain't worth it even if you can make it work.