Use your points and get either 2-2 bedroom units ,or a grand villa and a 1 or 2 bedroom unit.
That's what I'd do too. We tried offsite for the first time last year and it just wasn't for us. These are my reasons--like always, a lot of this is specific to my personal preferences, so YMMV, but sharing in case any of it resonates:
1.
Transportation After being spoiled with the "bubble" of onsite transportation, renting a car was a pain. It was expensive, and the rental process itself was time consuming (and I suspect that will only get worse once magical express goes away). I really disliked driving everywhere--we found the whole disney area very difficult to navigate by car as our GPS kept confusing what roads we were on and we had to backtrack, and we accidentally wound up in Disney-cast-member-only areas as couple of times as we got lost. As soon as you left Disney property it seemed everything was a toll road so it was a pain to know a wrong turn just cost us another $8 fee from the rental company. Onsite, transportation wasn't always efficient, but at least it was easy. Also, don't forget you'd also be paying for parking at the theme parks if offsite, which can add up since a big group like that would need multiple cars.
2.
Accommodations: It was our first time using airbnb, and I was super careful to go with an option that had nothing but five star reviews (and plenty of them), and paid above average rates to make sure we got a nice place (roughly same cost as onsite, after all the fees are added in). The place was exactly as pictured and looked very nice, but it became pretty clear that it was a money-making enterprise for someone rather than an actual vacation home the owner stayed at. I think a lot of places in central florida are like that. The beds were the least comfortable I've ever slept on and the linens were scratchy. We had to go shopping for things you take for granted in an on-site stay (e.g., toilet paper, soap). The internet was not functioning, at all, and I needed to be able to work in the mornings, so wasted hours sorting out with the owner getting it fixed. They were nice about it and to their credit did find a solution, but not how I want to spend my vacation time. I also felt like we were constantly on edge worried our kids would damage something and we'd be on the hook for it.
Some of this is bad luck, but I do think there is a risk you run with a vacation home rental--you don't have the same level of assurance of quality that you get with Disney, since no matter how much time you spend researching options, there's only so much you can tell from the online listings.
3.
Dining: If you want to book any TS dining, onsite advantage would be critical with a large group. We've never booked for a group that big, but with a family of 5, we really need that onsite advantage of 60+length of stay. I also really missed the convenience of being able to pop to the resort dining places for a quick hot breakfast I didn't have to cook, nice cocktail in the evenings or by the pool etc. Even if you are used to getting groceries onsite, losing the option of onsite dining altogether was something I missed.
4.
Amenities: Sure, you can get a house with a pool, but it definitely won't be the same as a DVC resort pool. We spend a lot of time swimming and love the themed pools with slides/splash pads/hot tubs you get at Disney World. I also really enjoy the poolside entertainment (trivia etc.). Our rental came with a pool but even though it was advertised as a heated pool, the water was freezing (it was October) and the pool itself was a bit small and basic, so we only used it once.
Edited to add: I also just remembered the 30 minute early access for onsite guests will be ineffect during your stay, so if you like to rope drop, onsite is a must.
