It can be difficult, but it's not impossible. We (Pinhead family) expect to earn 4 certs from a single four-night stay. We're booking two rooms, total, and have it jiggered so that each family member is registered for two one-night stays:

Room 1
1st night: ZtP (me)
2nd night: Mrs. Zippy
3rd night: ZtP (me)
4th night: Mrs. Zippy

Room 2
1st night: #1 child
2nd night: #2 child
3rd night: #1 child
4th night: #2 child

We'll book somewhere for a weekend, two rooms, and burn all 4 certs at once.