Children’s chapter book about secret agent grandmother with reversible cover 2015-2017?

[Darcey]

I’m looking for a book I used to have but never read. Probably 2015-2017. If I recall correctly it was called something along the lines of “secret agent grandma” or something. The hardback cover was yellow and it had the grandma sneaking around on it and I think the boy and girl kids. It also had a dog I think and maybe windows and/or a couch? The dust jacket was reversible and the inside was red and called like “the art of napping” or “how to take a nap” and had a fake author name. It explained that it had a fake cover because they were spies and didn’t want to be discovered. Anyway, it was about two kids (a boy and a girl) who went to stay with their grandma I think (just for a visit I believe) and find out that she’s a secret agent and try to help her solve a mystery (possibly a dog napping or something to do with stolen money). I think it like spoke to the reader basically and broke the fourth wall but wasn’t a choose your own adventure thing (I might be getting this confused with something else tho). It was a children’s chapter book that was mostly words but had occasional illustrations.