Those all look like the same weight to me. Except for the really tall one at the end who looks heavier, and the one next to her who looks lighter but I would put the others as around the same weight.
I wouldn't be muzzling a horse that is the weight of the second photograph unless they had metabolic issues. Muzzles are a last resort IMO. Essential for some horses but best avoided when they really aren't needed as in the case of your horse, OP.
I much prefer the second picture. However, I would want to check his saddle because it looks like he may be getting some muscle wasting behind his withers and either side of his spine that isn't there in the top picture. It maybe a trick of the light though.
One of my yard dogs really loves a balloon. Though the horses aren't impressed, and nor is her sister, Molly! (Molly is much more sensible and doesn't play very often). Here she is playing with it safely inside the house. Feel free to share!
https://youtu.be/MjAUpsK0snE
No, I don't like the video either. Couldn't watch it until the end. Horses in too deep water to be dosing. Children are in danger doing such a stunt. As a parent, I wouldn't allow it, let alone film it.