No idea about Kirby, but they do make a wax for dog paw pads (used by sled dogs) that may be helpful. It is Musher's Secret (and there are probably other brands out there)
The only thing I could think about the blood in Kirby's urine is possibly the kidney's being overworked trying to process all that salt from the water. I honestly don't have a clue, but that's what I would have thought. I sure hope Kirby is alright, and it isn't anything serious. Let us know how things turn out.
As for Franklin, Tomahawk also tends to get sore paws since he likes walking over sharp and pointy rocks. Whenever I see that they bother him, I put some musher's secret on his paws and wrap them up for like 15 minutes so he doesn't try to lick it up. It seems to help him out, but it's possible that Franklin has more sensitive paws. Poor Franklin. :[
When humans do one of those body cleansing things to clean out their system, they would sometimes do a salt water flush. Drink 8 oz of water with salt and everything the body will be gone. It will exit the body violently. The sheer force of it can probably do damage to the toilet.
Any how seems like Kirby might have given himself a bowel cleanse.
But as for the blood, I don't know. I just hope there wasn't any damage to his kidneys. I heard if you punch a human hard enough in the kidneys.. you can force them to pee blood.
Hope everything is ok with your pups!
I don't have any ideas for the issues you listed here, but I was wondering how Kirby and Frank are doing in general? Has Kirb settled into the new flat?
Blood in urine can be trauma / infectious / inflammatory. I'm gonna rule out salt water / kidney link, not that it can't happen, just not within that short timeframe.
As far as paw pads goes, avoid wet sanding them is your best bet, musher's secret helps, but you'll need to apply it generously and get them in real good. Vet wrap them before activity? just a thought.