@WannabeYeah, overly helpful moms could be an exciting theme, especially if said moms do that slightly reluctantly or inadvertently or are otherwise confused about the exact state of affairs in the couple they're helping along. But the rest of the mega harem family background just comes as unnecessary unnatural and overblown.
I would rather see two more or less ordinary very shy and/or reserved teenagers go through a slow and complicated romance with one or both having empathetic family members helping out from the down points and errors, but in the process come to opinion that the couple are just especially good at hiding they have sex -- not that they're not there yet at all -- and act accordingly to this mistaken perspective effectively encouraging the youngsters to take the leap into the physical.
Resulting into something like:
Alice and Bob have some common interests or just intense intersecting of lives, and been all but explicitly dating for quite a time, in just about every bystander's understanding. Seen as "cute couple" one or both of their respective families are all but married them off already, although internally they're rather in danger to fall in friendzone on one or mutual directions.
So the situation with Alice staying overnight at Bob's house may not at all be premeditated by Bob or Alice themselves, but arise spontaneously out of practicality in some situation not necessarily strongly linked to their ongoing relationship, while there's very little outside resistance to the idea.
Lets say, upon arrival, Alice drops her bag in Bob's room before his mom may cordon her to the guest room in the hurry and uncertainty of that situation. The question where she would sleep doesn't arise until much later in the night, when finality of her staying over becomes apparent.
[Bobby pov]
"So, Alice, you're staying over after all, yes?" Mom asked.
"Well, yes, apparently," she confirmed again what had been seemingly long decided by now, "Unless..."
"No, no, it's not a problem at all, as I said. Now, only, where would you sleep? We may..." Mom trailed off seeing us exchange glances and blush in unison. She probably was about to offer some kind of choice, between the guest room and what, my sister's? "Well," she sighted, "okay, but Bobby, you will need clean sheets."
Saying that she went over to the closet, produced a set of bedclothes and promptly gave those to Alice. Well, she was closer.
Alice barely contained her jaw dropping to the floor with a bang, concealing that under a wide smile. "Thanks Mom," she blurted.
I tried to quickly calculate what my reaction should be if this had been the planned outcome all along, and decided to echo that.
"Thanks Mom," I said, my voice weaker and softer than I expected, but Alice's eyes said I haven't blown up the situation yet. So I put my hand around her hips and led her towards the stairs. She leaned upon me, her knees failing in what appeared to be a fit of dizziness.
"Good night," Mom seen us off with a type of smile I haven't really seen yet, not in context of me anyways.
"God night," I echoed automatically. Alice just nodded.
Up in my room it was perhaps Alice's woman's practicality setting in to suggest we don't actually need the clean sheets just right now yet.
***
And that's how they both lost their respective virginity.