Hi Leri
I would have probably given it a go and tried moving a couple of the strongest piglets from the first litter. I have no doubt that sow number two would have accepted them - but after two days with 'Mum' the piglets might not have felt the same way. If they latched on and started feeding straight away then brilliant otherwise I would have given it half an hour to an hour (staying with them to avoid any 'accidents') before giving up. The older piglets would by now probably be stressed and making a bit of noise and sow number two would be getting stressed and anxious too when she should just be flat out, resting and feeding the piglets.
Our 'house reared' piglets were 8 days old when we introduced them to the second sow. They were pretty small and actually around the same size as the newer piglets. The second litter were less than 10 hours old when we introduced the older two and they didn't react at all to the new additions
.
So, my answer would be give it a go, but don't ruin things by persisting for too long. Pigs are designed to deal with large litters and sometimes it's best just to leave mother nature to it. Over the years I have interfered less and less with the farrowing and have had greater success (and more sleep!)....the pigs definately know what they're doing. That's just my opinion, I'm sure others would advise you differently.
Glad to hear everything worked out well with your piggies.