This sounds like a very difficult situation, and I regret that you have had to cope with so many additional challenges when disciplining your daughter. Teaching children limits and the consequences of their behavior is tough enough without having to deal with family members constantly questioning your decisions.

I think that the next step is to gain better alignment with your husband on discipline. I cannot emphasize enough how difficult it is for children to experience their parents as inconsistent and disagreeing on what is appropriate and inappropriate behavior. It creates a very unsettling anxiety within children (it would be troubling for anyone to never quite know what is expected of them). Parents of children who disagree and fight over consequences tend to have children who act out more (talk back, hit, bite, "not listen") because they are overwhelmed with the stress of inconsistent parenting. Firm, but loving consistent parenting is actually quite "holding" and reaffirming. "Ah, yes," the child thinks. "I know exactly what is expected of me." This is very reassuring for a child.

Thus, you and your husband (without the input of your mother-in-law) should sit down and discuss some of the common behavioral issues you are noticing in your child BEFORE he gets into trouble. Come up with a list of consequences that you can both agree on and implement them calmly, lovingly each and every time that behavior is exhibited. If there is a disagreement between your husband and you, commit to discussing it later when your child is not around. You should never disagree in front of your child.
 
As for your mother-in-law, you and your husband should agree on what her role will be. Given that you are living with her, she may have more influence on parenting, but it should be agreed upon. If you imagine the confusion your child has with two parents disagreeing on appropriate behavior, consider what it must be like for a child to have three "parents" who cannot agree. Thus, decide with your husband what kind of involvement your mother-in-law will have in the parenting process.

I know this will not be easy, but if you stick to some of the key principles of parenting - mother and father remain consistent, in alignment, etc., I imagine that things will go much better.

Good luck.

L. Compian, Ph.D.
Counseling Psychologist
Education.com