I agree that two rooms is still way too tight!
Since you have three families basically, I would look at three rooms.
The value resorts would be the most economical. Spring discounts aren't out yet, but likely something will be offered!
Spring break varies widely, so any time you're there during the spring, it may be someone's spring break.
Not sure if you are flying or will have a car, but also the Disney Springs hotels can offer more affordable rates. The don't offer Magical Express though, so if you're flying in you would need to arrange transportation from the airport and factor that into your budget! Your daughters may like the look of the Doubletree Guest Suites, and may decide it would be okay to share one suite, though. Each has a bedroom with two queen beds plus a sofa sleeper in the separate living room. I've stayed there many years ago with my parents (I was an adult), and I took the sofa sleeper. I've also stayed there for one night with my kids and husband. It's not quite a "resort" but a fine hotel for sleeping. The Holiday Inn gets good reviews too. The bus service is adequate, definitely not quite as frequent at the Disney resorts, but not bad at all, and MUCH better than most offsite resorts.
If you did an offsite house rental, you would need two rental cars or an 8 passenger van, but that would be challenging as you'd all have to keep together. I would rather have Disney do the driving, so wouldn't go that route.
I am already booked (did it a couple months ago) for next spring break. Without discounts, our room at Pop Century is running $195/night weekend nights and $160/night during the weekdays. I'm hoping for a discount or deal through an agency at a deluxe resort, but at least have that booked for now.