I have had two sows pig outside and in very wet conditions. The first Sow had 13 piglets 1 month ago and 10 survive. The three that died did so within 24 hours of birth and it probably had a lot to do with the bab weather at the time.
The second sow had 10 piglets and again 3 died in similar cirscumstances to the above. These are now 1 week old.
All are now well and and they are thriving.
I would think that if Grahams' piglets have somewhere dry to lie and sleep, and they are feeding well enough from the mother then all will probably be ok. If they have survived thus far then there is probably little to be gained by bringing them in at this stage