Horse Health And Care?

I Have 8 Horses . And Last Winter Was Kinda Ruff I Went Thru A Ton Of Hay .. Spring Came And I Have 2 Horses That Are Under Wieght ... My 2 Year Old Mustag Brandi You See Hip And Back Bones ... And My 2 Year Old Gelding Mustang Wrangler You See Everything .... I Have Wormed All 8 Of My Horses Every 3 Months And I've Been Feeding Them 3 Times A Day And They Get Wieght Builder And Magie Cell .... Now They Have Put On A Little Wieght But Idk What Else To Do ???