Re: Husband and daughter
If your daughter is 18 now, then she is a consenting adult. However distasteful this is, it is not illegal. Still, you do absolutely have the right to divorce him on the spot.
Is there reason to believe that this was going on earlier? If so that is illegal and he can go to prison for a long time.
Do you think she is truly doing this of her own free will or has been coerced in some way.
Even though as an adult she may have made a choice to cheat with your husband I think protecting ones children still takes precedence, but I can see other viewpoints.