Something inoticed about my 4month old

Her legs are always bent at the joint of her knees wheb lying down she keepa her legs a liitle bent and watever i try its naturally like that.where her joint folds are, its a dif colour and looks like a red zakhm. Also when i try to stand her up she stil stands with her legs but bent again…normal or not?? Another thing is she seems to be taking out lots of milk she doesnt drnk tht much she drinks less than her recomended allowance so why vomiting out so much milk?? My fil says to dilute the milk which i thjnk is wrong so havent done it.