Shortening a dress isn't a matter of hemming it. The dresses in the OP probably could be shortened at the hem, but many dresses can't.
If the torso is too long, neither dress could easily be shortened.
The styles and fabric do not lend themselves to major alterations.
why not go physical shopping and try things on and lunch with a friend. Go with a blunt, honest friend, not one who would say you looked lovely in anything.
I have a friend who will say 'that style/colour is wrong for you' but my mum would say it looked lovely.
The 'lovely' item would be worn only once and I'd have cringed at the photograph and consigned it to the charity shop.
The item bought with honest friend would be still in my wardrobe and still being worn.