I would be totally pissed if I were you.
My BFs parents took care of my Poppy while we were away and they hadnt cleaned her eyes at all in those 2 weeks! I came home and she had eye pancakes
I know how you feel because I was so angry when I saw the state of her little eyes, but it was a very kind thing they did looking after her while I was away so I didnt mention it.. I just cleaned them myself.
I would ask your brother to tell you EXACTLY what he has been feeding her when you were away, you need to know if anything could have poisoned her.
It could well be the change of food which has upset her stomach so keep an eye on her and if it dosnt get any better I would take her to a vet.