Yes, swiss chard is fine everyday in moderation. I would give only 100 grams or less per pig. It does have more A than anything else so that's why you need to feed in moderation.
On parsley, if you have young piggers (under 6 months), you can get by with feeding parsley in small amounts daily (2-3 sprigs) as youngsters need the calcium to grow, but it can start causing problems in older pigs. Piglet, if you are only giving one sprig per pig a day of parsley, that's ok.