K.A.
Babies go through cycles where they sleep longer and then begin waking more and then go back to sleeping more. Growth spurts, teething, working on and meeting milestones, physical and mental developments all contribute to various cycles of sleeping.
At 4 months old, waking 2-3 times a night is 100% normal.
I would never in a million years hire someone to teach my baby to go against human nature!