Hi,
The first time we went,DS was 8 and DD's (twins) were 6, a little older than yours

We stayed in a hotel, SIL came aswell, and we had interconnecting rooms. We found there still wasn't enough room for them, and they drove us mad running round and round through the interconnecting door. Also, they were tired when we came back, and either fell asleep or didn't want to go out;and then when we did get out, we had to drive to find somewhere to eat, and they would be grouchy because they were hungry!
The following year, (yes somethings must've been good because we went back!) we stayed in a condo, and it worked really well. We were near the swimming pool and playpark, and (really boring I know

) I had a washing machine and dryer! We didn't have to drag them out if they were tired as I could cook, or we could get take out and eat it at a table instead of on the bed! Also, there was space to relax.
The following year we had a villa, and I didn't like it so much, but DH loved it. I felt the kids, (10 and 8 by then) needed more interaction with other kids, which they got the previous year using the communal pool. That of course wouldn't be such a problem for you as your twins are only 4, but I personally found the villa holiday too insular. There were no local shop to walk to, and as I didn't drive when we got back, that was it!
Now the kids are 17 and 15, we prefer onsite, as they have more freedom, and can even go to the parks' together using the disney transport.
Hope this helps,
Jules x