Hi Eden,
The Value Resorts are the most economical places to stay on site. You could get one or two rooms at
Pop Century or one of the All Star Resorts. Those rooms sleep four plus a child under the age of 3 in a pack 'n play crib. If the two younger children that you mentioned are over the age of three you will need to reserve two rooms in a Value resort (you can request connecting rooms).
Another option is
Port Orleans Riverside Resort. Some of their rooms have two queen beds and a pull down trundle bed. My 9 year old could comfortably sleep on that bed. The maximum occupancy on those rooms is five. If you need to sleep six, you could reserve a
Cabin at Disney's Fort Wilderness Resort. However, it is cheaper to rent two Value rooms than one cabin.
As far park tickets, it is cheaper to buy Base Tickets as opposed to Park Hoppers. This will allow you to visit one theme park per day. There is so much to see and do in each of the parks that you don't have to hop from park to park to enjoy yourselves.
I am out of room, but if I can help you further please do not hesitate to let me know .
Wishing you a wonderful vacation,
Kaylene