Hey dpaortz, as Diane explained you above, the guide 0104 explains: "If you need more space, attach a separate sheet of paper".
Then you choose whether you:
a) Add the same page, include the same information and add the parts in the name that didn't fit or;
b) Attach a blank sheet of paper with your name, the specific field you're referring to and add the lacking information.
It's up to you.
In my experience, when I was filling up the additional family info form, there are only 3 spaces to add your siblings information, and I've 4. They specify that you attach a separate sheet of paper. I filled up the first one with my 3 older siblings and then a second one exactly as the first one at the previous fields and adding my younger sibling, and the other 2 remaining fields (for siblings) I wrote "Not Applicable" so it wouldn't be blank (as they were specified on the first page)...