Now father can claim his custody from court. You don't need to pay the 8k now as you are taking care of the child. If the in-laws are taking care and you don't need custody the child support can be fixed as one time lump sum for his education and well being. Otherwise monthly amount can be mutually fixed between in-laws and you. If there is no mutual agreement then you can approach court and as per its direction you can do the needful