First,
You'll find this is a well debated topic. We're a family of 5, including a set of twins too. My general response, and I'm not kidding, is that I wouldn't stay on property even if it were free. Not gonna happen. We love our space. We rent offsite and at the bare minimum get 3 bedrooms and 2 bathrooms. Often, we'll get a 4 bed/3 bath townhouse. We pay anywhere between $600-$850/week, including all fees and taxes. The places are usually between 800-1200sq ft. It's beyond awesome to have separate spaces for the kids to go, a full family room, full kitchen, in house laundry, privacy
and many other things. No, you don't need to "cook" or "clean" if you don't want to. We pay a cleaning fee, so beyond normal picking up after ourselves, we don't dust, vacuum, etc... And you can cook as much or little as you want. Even if you don't cook, being able to go to a grocery store and buy quick snacks and things is awesome.
For us, the "negatives" others will list are actually "positives" for us. We don't eat in the WDW restaurants, so the dining plan would be useless (plus I've heard it's debatable if it's worth it anyway). The Disney "bubble" for us is much more than just the parks, so we see that as a positive. There are so many things just outside of WDW...shops, restaurants, etc... Having to use/rent a car is a great thing for us. No way would we rely on WDW buses. We like to come and go when we want, where we want. Having your own car gives you so much freedom. Making FP+ at 30 days is no big deal at all, with very limited exception (FoP).
But that's just our opinion. There are tons of people who would strongly disagree with me and swear by onsite only. I can fully understand why they feel that way and if it works for them, terrific.
There are TONS of choices just off WDW property. Look at sites like VRBO or AirBnb. Rt. 192 runs right outside WDW property and there are more choices there than you'd know what to do with.