Do we need ushers?!

They all do the same thing really so you can either call them all ushers or groomsmen but the term ushers tend to be used more often at a Church ceremony rather than a "venue" ceremony where they are more commonly referred to as groomsmen instead.

They can be a way for the groom to give "rolls" for close friends and or family in much the same way as bridesmaids for the bride.

If you already have 5 groomsmen, you might not need additional ushers just have them double up on duties to keep things simple.