I believe it was initially, but I’ve always thought it was to get him out from under their feet. Imagine him drifting in and out of your house, stopping by to get his washing done, eating you out of house & home (allergies all catered for obviously) like the stroppy teenager he probably was.
I also think the reverse of you @C’est moi. I think after the initial shock of the ‘romance’ and after meeting Fanny, they realised the horror show unfolding. I think they keep visits to a minimum and off camera because they’re not comfortable being associated with Fanny and only comply to keep a check on Snorts. Quite what they make of the non stop shopping, holidays etc is anyone’s guess, but assuming they have an ounce of sense, they are hoping that it’ll all end sooner rather than later, but there’s nothing they can realistically do about it, and are hoping the ‘romance’ will run its course.
In a nutshell, what Parent would want Fanny anywhere near their Son, age gap aside.