I would talk to your daughter about the tickling and teasing. I have three older brothers and was tickled unmercifully but there was nothing sexual in it, you literally can be tickled to death and often tickling itself is not fun/is painful.

I would then talk to my ex-husband and tell him to "control" his brother, that the tickling has to totally stop and you don't want to hear about your daughter crying from teasing. I would then monitor, through your daughter, how they behave.

I would only involve CPS if your daughter indicates the touch has been sexual in nature and/or things don't go well this weekend (tell her she doesn't have to like his tatoos, you don't either). How old is the uncle?