Hi. Unless they have a court order, they have nothing to say about how you raise your daughter. Obviously if she is too young she need a Babysitter but someone with suicidal tendency is not suitable for this task (perhaps this is what was hinted that she was let alone as in the other person can't be considered a reliable custodian).
Now, how to handle in laws. It is never good to have trouble with relative but you really need to stand over them. Let them have some liberty but make sure that they know that you do them a favor and that they should not take more than allowed. Then be very clear on what you don't accept. The name of the game here is respect and clarity. Also never talk loudly to them even if you are angry, be very kind but also very firm at the same time.