As above, have had no problem doing this at all.
In fact reception at the Fontainebleau Miami (only mention the name because their charges for everything are in the ridiculous zone so I would have expected some push-back!) just asked me how many key cards I wanted and when the wife and kids turned up at the weekend I was able to get pool wrist bands for them all too.
As mentioned, just book a suitable room for 4 people.

In reality, in the US anyway, almost everything can be resolved with some money across the desk at check-in.