Look. Look. I am as invested as the next person in a nuanced, well-developed exploration of the fractured relationship between the college trio, but I contain multitudes, and also just really need more AUs in my life where Maddie actually knows Vlad is now a ghost loser simp intent on getting Jack out of the picture and plans on ctrl-v-ing himself in his ex-best-friend's place like a badly photoshopped family picture, because I think this has the potential to be absolutely HILARIOUS.
Neither of them tells Jack because Maddie can't bear to break her husband's heart by revealing the truth about their long-lost friend, and Vlad won't tell him because, on top of the obvious reasons, Jack also keeps inviting Vlad to stuff. Family dinner? Danny's school events? Camping trips? It's remarkably convenient as it puts him in a great position to play Uncle Vlad until he can successfully enact his bonkers plan.
Except now, in addition to Danny knowing Vlad is up to no good and being very much not on board with the Fruitloop's whole shtick, Maddie's in the same boat too. But Maddie and Danny are keeping this info from each other because she still doesn't/can't know her son is Phantom and if Danny outs Vlad, Vlad will turn around and spill his little secret too. And for Maddie's part, she probably just doesn't want her son knowing that Vlad is a ghost. It's a bad look to admit you've welcomed a specter from the afterlife into your house (on multiple occasions) when you've spouted off how dangerous these creatures are since your kiddos could walk.
This sets up a scenario where you've got Jack: oblivious, Danny: trying not to reveal his secret while also keeping Vlad from murdering his dad, Maddie: being a badass ghost hunter protecting her family and blasting Vlad into next Tuesday every chance she gets, and Vlad: just, being very...Vlad about everything. Chaos and hilarity ensues.
Jack's humming to himself while making dinner, back turned, unaware anything is amiss as Maddie saves his life, firing a blaster at Plasmius and sending him through a wall before he can attack her husband. She immediatley hides the ecto-weapon behind her back, giving a too-enthusastic "how was your day sweetie!" when Danny walks in the door, brows raised. Jack turns around at the interruption, giving a bright, oblivious, "Where'd Vladdy go?!" which prompts a groan and a "that guy's here again?" from Danny.
Maddie and Danny can bond over their shared aversion to Vlad's general existance, though neither of them admit there's a little more to it than just "he's an arrogant asshole." Or, better yet, they're both putting on the facade, keeping up pretenses, pretending they don't despise the dude, because how are they supposed to explain why they despise the dude? Vlad is impossibly amused by the whole song and dance they're doing, because of course, he's the only one who realizes that Maddie and Danny both know he's a half ghost and are keeping that from each other. And like, as if he's going to let them in on that little tidbit unless it directly benefits him.
Sometimes Maddie and Danny run into awkward situations where they're both trying to protect Jack, but they don't realize it, and they can't be overt about it without the other person realizing what's going on. "Don't you have homework? You go do that, I'll check on your father and...uncle Vlad." "Oh, no, no, don't you worry about it, you're so busy, Mom. I can go check on them!" "That's really not necessary. I don't mind at all." Meanwhile, Vlad is in the kitchen like "why don't you check that cooking oil with your face, Jack? Oh, I know it sounds unorthodox, but I swear that's how they do it in France."
