I think you're at that 'wonderful' stage of waiting, watching, wondering and waiting some more. The chestnut, I think she's actually pinto, did the slab sided to very round the next day in her last pictures so it's something to notice with her but not giving you a lot of info. They both look like they're elongating and both need to get more udder development, going by the book they aren't ready yet. Do you by any chance have fescue in your hay? If you do you need to take them off of it and put them on hay cubes. It might or might not have anything to do with the lack of udder, they could just not be there yet. Welcome to foal watch, exciting, exhausting and terrifying,
doubly terrifying for you. Wish I could be more help. There was one mare on here a couple of years ago who looked ready to go for about 4 weeks, cow patties and all, she got a little more udder and then finally foaled, after escaping out of her stall where the camera didn't see and having the foal in the back of her paddock alone, both were fine. Mare really is a 4 letter word.
Oh, duramectin (ivermectin) is the right thing for them.