I have a six year old mare that was a rescue... when I got her 3 years ago, she was 8 months pregnant and I had no idea she was in foal.... she was only 3, and a maiden.... and your descriptions above sound a lot like what she and I went through.... for like 4 weeks
I slept outside on a cot MOST of those nights... tail switching, holding, moaning, groaning, breathing hard, up and down and up and down.... I was so exhausted that the ONE night that I fell asleep while laying down with my son... she foaled. SNEAKY MARE! I swear she overcooked her for a whole month JUST so I would go in the house and leave her alone!! Im definitely not saying your girls not about to pop that little treasure out, but I know from experience how tricky they can be!!! Good luck! And I hope to wake up to 4 tiny hooves here!