Hello and thank you for using Just Answer. I am sorry to hear about the problems that you are having with your father in law. There is already tension because you have made it known to other family members that you do not approve of the tickling. The tickling in and of itself is fine but not so frequently around the diaper area. Also, it is unusual for a male to always want to change a diaper and bathe a toddler so often. He may just be trying to be helpful but since his actions make you feel extremely uncomfortable, you must confront him in a respectable manner. You may feel like screaming at him but try to refrain from doing do. Take him aside one day when no one else is around and explain all of your feelings. See what kind of explanation he offers. Make it known what you do not like and what you prefer...if anything. Your husband and other family members will probably be very irate that you confronted your father in law. But this is your daughter and you are concerned about her overall safety and well being. It is a shame that your husband is not backing you up. At least you will be moving out soon so the contact with your daughter will be curtailed.
If after moving out the behavior continues, call your local child abuse agency. I am not saying that your father in law has or will abuse your daughter. The agency will specifically be able to tell you what further steps to take, what to look out for, etc.
Another alternative is to seek counseling for yourself if your family seems to be turning against you on this issue.
Hope this has helped or at least provided you with some insight. Thank you and have a great day!!!