Kraklaw rebalances resistances periodically when it uses riptide eupnea. Biggest thing is keeping magic damage ~equal to physical. One MNK and 2 mura SAMs with buffs will kill it in under 3 minutes. If you have a mess of DD, formless off the bat and try to equal it out. One physical DD per 2 formless MNKs should generally be fine, assuming the MNKs are WSing. Requiescat/Mura DD are about neutral. Disengage anyone you can't balance, and have anyone who can nuke do so if you're still having trouble. It seems to not have a zero-sum, if your damage is balanced both physical and magic will end up doing more than normal.
Krabakarpo builds resistance proportional to damage taken. If you do 50% of it's HP in purely physical damage, it'll have -50% physical damage taken. If you do 90% of it's hp in purely physical damage, it'll have -90% physical damage taken. This is entirely seperate from the TP moves, if it has scissor guard up and it's been taken 100-10 using only physical, it'll take only 1% damage.
The best way to handle it is to bring murasamemaru or requiescat users and keep physical multiplier low enough they can still hit above 0 with scissor guard. Personally, I formless at 60%(this won't do amazing damage or carry you, it'll just slow the physical penalty by building the magic one) and have all DD that aren't using requiescat or mura disengage(also at 60%). This ensures you don't take the physical multiplier too high. As long as you're still hitting above 0 for TP, it'll die relatively fast to req and mura.
I don't use sulpor at all, SCH/RDM enthunder is superior for shark and will allow your MNKs a real subjob. If that's not practical to you, I would advise using it on both crabs. Make sure to lunge it off before the pugil, so as not to accidentally superbuff it's enspell.
