Every time i perfectly skin my character's thigh and i mirror it some weights still remain there and make it not look properly

so this is before mirroring https://gyazo.com/5a85d80ae966fd436e3f7eec4fd3df00

and this is after https://gyazo.com/dce36ca2bec473065f74cf11bf6a52c2

is there a way to prevent this???

also how do i properly distribute the weights form the hip and thighs???