One of my pigs has a prolapsed penis following him being neutered by the RSPCA before I had him (normally they are retracted unless they are in use) because of this he gets himself in rather a sorry state and has to be bathed frequently. He always seems to quite enjoy it! I've put him in the bath, a bucket and a paddling pool and although I've never put him in water so deep he couldn't touch the bottom I've seen him swim a few times.
It's quite easy to tell if a pig is scared and the ones in the clip don't look, or sound scared to me.
Years ago , one of our 'homebred' piggies was a keen swimmer. She went up'n'down the bath, we always put a folded towel 'island' at the shallow end for her to rest if she wanted . But she swam for Britain.
Maybe give them their bath then refill the bath with clean warm water (just in case they get water in their eyes, clean water is better than soapy) but don't let them hear the water running if it's loud. Then if they're relaxed let them try.
Our boars sat at either end of the bath with that 'look' that we knew they were considering jumping . (Careful with the plug chain in case the tangle)
You might end up with Olympic Standard Swimmers? Or not