I mean yeah, but also Dreamtarou says that he dressed up like that cuz of her love for Shizuka, and since it's actually her subconscious taking the form of Dreamtarou. I do see the mother/daughter thing, but Nano also almost confessed during the floating island arc when they thought they were gonna die. all that just to pivot to a mother/daughter vibe would be strange, not to mention having that kinda relationship with someone your in a polyamorous relationship with is kinda weird, especially especially since her moms alive and they're on good terms now
If I was about to die, I would say "I love you" to my brother, mother, sister, cousin, niece, nephew, uncle, aunt, etc. it doesn't mean I love them romantically.
He didn't dress up because of romantic love though, he dressed up because Nano adores the cute little Shizuka, it never said in what way she loves Shizuka in the dream, and I think Nano made it very clear in what way she DOESN'T love Shizuka in the dream.
Also Hahari has her actual daughter Hakari in the harem, and she definitely has a mother daughter relationship with her, so is it so weird for Nano to have one with Shizuka?
Also no member of the Rentarou family is required to love any other member besides Rentarou romantically, and some of them very much don't, such as Miss Naddy, Uto, and well, just the majority of them really.
And finally, her mom being alive and on good terms only happened recently, and Nano can still act like a mother even if her mom is alive and on good terms, people can have multiple father figures and multiple mother figures, even if they aren't their actual father or mother.
P.S Nano immediately confessed and hauled Rentarou into a kiss when she was convinced that there was a point to romance and she was in love with Rentarou, if she actually was romantically interested in Shizuka, I doubt she would hide it, and she hasn't shown an ounce of romantic interest so far, sooo....