I think we all agree for this childs sake you need to ask for some help here, too many questions come to mind ...let others find out what is happening if anything ,they will know the technique used to question 3 year olds ...
I agree 100% with Cherie...get social services involved IMMEDIATELY! If the girl and your son are being abused it needs stopped now. And like Amanda said I would also stop visits with the father until things are situated. Also get your son in to see a child psychologist. S/he may be able to get your son to open up about things.
Good luck!
Stop your son having contact with his father before it goes even further, even if it's not his father that touches him in the places he's not meant to it could be someone in his family he has admitted to his uncle touching him. When talking to your son about it tell him he can tell you anything and you won't be cross with him what ever he tells you. You need to get him to open up to you somehow, tell him he doesn't have to be scared to tell you. Phone social services let them know what you know about your sister-in-law (you can be anonymous you don't have to tell them your details). Let the police know what your son told you, they can follow it up and someone there can talk to your son see if he will open up to someone else.
With the girl there could be a lot of reasons why she's sharing a bed with her mother but she shouldn't be wetting the bed at her age.
call social services and report this..you will get no truth from family members and it will just cause chaios....protective services know how to get to bottom of these things...you can be anonmnus (sp??)
you may save this girls emotional and physical life, please call
Id get a lawyer for son....insist on supervised visitation and get son into counseling they use play therapy watch how kids play w dolls, toys draw pictures its all analized....dont let that little boy back over there all signs of
serious abuse.....he admits uncle touched him .Police should have been phoned that very minute...all of this screams sexual abuse...stop it before it befomes full penetration....
maybe young girl sleeps w granny cause grandma knows and is trying to protect her?