The bent cross-members are not a safety concern. As long as they support the floor and you're comfortable walking around in your trailer, they're fine. I'd replace them if I was planning to do a frame-off repair, but otherwise probably leave them in-place.
The tears at the bumper are not too worrying. I'd take the trailer to a friend who knows how to arc-weld, patch the rents and add "L" plate gussets on either side of the bumper-to-frame connections.
If you decide to do a frame-off, get the frame sandblasted and inspected by a trailer frame welder. I'd suggest taking it to a place that maintains and repairs farm equipment, as they're often better welders and more moderately priced.
Either way, your frame needs to be cleaned and painted. If you do a frame-off and take it to a shop, have them paint
it. If you leave it in-place, then you need to wire wire-brush it clean to remove any loose flakes and use POR-15 rust preventer. It's expensive, but it's the best product on the market for a frame with existing rust.
The cracks at the wheel wells suggest your floor may be rotted. If that's the case, it's a really big job to fix it. You basically have to gut the trailer, chip the floor out, then install new plywood and fiberglass. Big job. Been there, done that, hoping not to have to do that again.