Timeout doesn't work 👎🏼

Okay I babysit some toddlers and this 1 toddler just recently started talking back and telling me no!  Now the timeout doesn't work so now what?  Plus she tries to jump over her sister who is trying to learn how to crawl and sometimes lands on her!!!  I have mention it to their mom several times and she doesn't tell me how to resolve it!!  My hands are full 🙈