I am married with 3 of children with another man and 1 with my husband. My 3 year old doesn't know his dad and calls my husband dad. His real father talks to the other two children but my husband and I are looking to see if my husband could adapt my 3 year old. How would I do that?

You will have to get the real fathers permission to start with... you will have to go through the courts for the adoption process... so you will need a lawyer familiar with this process to start with. If the child's father agrees, the process will go smoother... and that's a very relative term... because it's a fairly complicated process.