Helencus,
It is illegal to bury dead piglets - they must be incinerated in a licenced incinerator. You can take them to the local hunt, who may charge you for disposal, as they will have a incinerator. Otherwise you can join the fallen stock scheme and a member of that scheme will take them away, again charged for.
If you are breeding regularly, it is worth getting a freezer and freezing piglets until you have a collection, as there is a minimum charge, think ours is currently around £30 for a collection.
Little Blue - thanks for sharing your experience, and posh house ! Since there is an upstairs window, presumably they go upstairs to bed??
On mummified - you will never know the cause, could be lots of things from stress, diet, some trauma, being frightened, piglet jut not developing normally etc.etc.
Helencus, one thing that little Blue says reminds me - if you do either farrow together or put mums back together afterwards, they will "share" the feeding, and piglets migrate between the two. In practice this generally means that one mum ends up feeding all the piglets, loses lots of condition, whilst the other dries up and gets fat !
Also note when piglets stop feeding (either because you withdraw them, or they wean naturally, or as with little blue one dries up), then they will come straight back into season a few days later - so if boar is still in there expect your next litter to have been started! If your pig has lost condition you may want to rest her before the boar goes back in. If she is in bad condition this can lead to poor ovulation, and a smaller litter next time. We generally rest sows for a months between litters.
Lots to think about !