I think it'd be funny if April doesn't find out that Delia is Ash's mom for a long time. Delia's not trying to hide it or anything, it's just that Ash had to get their tendency to not talk about themselves unless directly prompted from somewhere. Plus revealing herself to be Ash Ketchum's mother while she's staying in Lumiose City of all places probably wouldn't be a good idea.
You'd think Gallade would be a dead giveaway that she has some connection to Ash, but April's not from this world and thus doesn't have any of the context for Mutant Pokemon. (I mean it's not like Ash would've had any reason to tell her about their Gardevoir's past). It helps that they've been around for a while at this point, enough that there are now some trainers who have them, so anyone who's aware of how strange it is for her to have a Mutant Gallade would probably just assume the League's entrusted her with him (granted, they technically wouldn't be wrong) and thus wouldn't make the connection either.
Oh I love that!! It does make a nice bit of sense, too. Accepted, lol.

