How do i figure out which cruises do conjoined rooms/ book 5 people for a single room?

I am thinking about booking a cruise for my whole family as the kids christmas gift. Last time we just brought my then 9 and 11 year Olds. This time I'm debating bringing my toddler as well so we wouldn't have to find a sitter for 8-12 days. It's still debatable but I want to look into it as an option. Everytime I'm looking around on the site it only allows me to put 4 in a room even though it says 1-6 for a room. Or when I look for conjoined rooms it keeps coming back as not available on like every cruise I'm looking at. What do I have to do to make this work?