It was the OP's choice and mistake to buy a complex design that was difficult to self-assemble. Any number of simple metal bed frames bought online can trivially be assembled by a single person. Never give up your power unnecessarily.
Even if they have a disability, it still makes sense to get a simpler bed frame. The chance of anything going wrong when someone is assembling a simple metal frame are much lower.
As for pianos, they would have to get a dedicated piano mover.
