How to make my mom stop feeding my dogs food to make them fat?

my dogs marcelo and emilia are way over weight.marcelo weighs less then emilia because he excersizes more but it hurts when emilia excersizes.marcelo is about 80 pounds,emilia is about 95 pounds,they they are er spainel lab mixes.so onto the question.my mom feeds the dogs human food all the time,plus their regular dog food.if they wont eat the dog food she puts chicken in it.i know thats the reason they are fat.my mom and dad take them out to the walking trail every night,but it doesnt seem to be helping because they just keep eating.i really want my mom to stop but she never listens. please help!!!