Are you asking whether we think you should exchange the 11-lb. cylinders for 5-lb. cylinders?
I just purchased a Worthington 11-lb. cylinder, which is 9.1" in diameter x 16.8" tall. The Worthington 5-lb. cylinder has the same 9.1" diameter but is 11.9" tall.
Since floor space in the back of my rig and in my Bantam trailer is at more of a premium than vertical space I saw little point is purchasing the 5-pounder, particularly because the price was almost the same. However, I did note that the 5-pounder has a flat bottom vs. the steel ring on the 11- and 20-pounders. I am told that some people pick the 5-lb. cylinder because of the flat bottom - no tipping on any surface.
As far as propane capacity for weekend trips, I have used an 11-lb. Manchester horizontal tank on my Bantam trailer for many years. I have never come close to running out of propane for cooking and lighting even on week-long trips. I keep 2 disposable 1-lb. canisters in the trailer with an adapter "just in case," but have never had to use them. [Caveat: the 2-burner stove and propane lanterns in my '46 Bantam trailer are vintage low-pressure appliances, not high pressure units like Partner Steel stoves and the current offerings by Coleman, etc. Thus, even though BTUs are BTUs no matter the pressure, real world fuel consumption may be different.]
I have since added a Quikfire propane campfire to my inventory. I purchased the 11-lb. cylinder primarily for that because propane campfires tend to be gas hogs. Also, I wanted a conventional vertical propane cylinder for use when I don't take the trailer.
Since you intend to fuel a stove, grill
and propane campfire, I think two 11-pounders are appropriate. You should have enough propane, and you will be able to keep your essential cooking fuel separate from your non-essential campfire fuel in case you use more than anticipated. I doubt that you can get enough hours for an average weekend's propane campfire's use from a 5-lb. cylinder unless you keep the flame very low and restrict the number of hours that you use it.
You could go with 2 5-pounders plus a few 1 lb. disposable canisters "just in case," but why? You already have the 11-lb. cylinders.
Worthington 5-lb. DOT propane cylinder [9.1" x 11.9"], reg. $59.99 at CampingWorld.com:
Worthington 11-lb. DOT propane cylinder [9.1" x 16.8"], $56.97 at HomeDepot.com:
Manchester 11-lb. ASME horizontal propane cylinder mounted on '46 Bantam T3-C trailer: