Yes, you can eat them once they are plucked.
I expect all poultry have some lice burden - they get them off wild birds. We treat outs with a natural louse powder every ten days or so and dust the ark as well, when it's cleaned out. The way we do it is a two person job. I catch the hens - we do it first thing in the mroning so we catch them in the roost - fold in the wings and turn them on their back on a wee table. Lice are mainy found round the vent and under the wings - so Dan dusts those areas with powder. If there are any feathers with very heavy egg burden he plucks them out and burns them.
The lice on the pigs won't be the same as on the chickens - I'm pretty sure they are host specific - and I'm sure someone will be able to advise on the pigs.
Hope this helps