We use Shotts for our sheep. Where you take them in looks rather horrible - in fact totally grim - but the guys themselves are good with the animals and we have had no complaints of them at all. They have never lost any of our carcases and do let us have the skins and horns back if we ask.
For sheep you can take them in the afternoon before slaughter, there by 3, so they have an overnight stay, empty their bellies and stay nice and dry, which can be difficult at home. We prefer that to the mayhem in the mornings when there are trailer-loads of animals arriving, with a bit of vehicular mayhem, especially if it's icy. Sheep have to be in earlier than 8. Perhaps you could take your pigs in the afternoon before.
Our carcases are collected from Shotts by our local butcher, slaughter date to fit in with their own arrangements.
Ah, Ive just seen that you have to take them in on a Monday, so I don't know if they could arrive on a Sunday, but it's worth asking.