It depends on each appliance, but normally if the hose of the appliance has a regulator of some description built into it (see image),then there is a good chance a bayonet hose can be fitted and they are available in all configurations as well. But if you have a high pressure appliance, like the old Primus two burner stoves, or one where the hose does not have a regulator and connects directly to the gas bottle then you can't hook that appliance up to a bayonet.
You can only fit a regulated appliance to a bayonet.
Correct. If the bbq gas hose has a reg inline then it will work off the cvans bayonet as you will essentially use the cvans regulator (twin stage reg up the front near the bottles) because the bayonet to BBQ hose doesnt need a reg inline.
It won't work properly of you have another reg between the bayonet and your BBQ - for this reason make sure your appliance doesn't have a regulator built in to it (some portable bbq's do - like most of the ones that can run of disposable gas cannisters...
If anyone needs a hand PM me the exact model of BBQ and if you have and a photo of the gas inlet fitting (where the hose fits onto your BBQ send that too - I'll yell you what you need get to make it work.