Well this isn't always the case, but whether it is 2 motorbikes or 100+ you have to consider lot of different things.
Some some simple tips for riding in a group.
The first thing I always tell people is, NEVER ride out of your own comfort zone, do not try to keep up with someone if it makes you feel nervous, ride to your own abilities, if you are in a group your "friends" or fellow riders will wait for you at the next junction if you have not managed to keep up. If they do not wait for you, you have to tell yourself are these the people I really want to be riding with? Remember it is not all about the bike it is all about the rider. I have been out with many groups and to be honest, some ride a lot faster than I do and no, I am not going to keep up with them, Likewise I have ridden with people that ride slower than myself, do I bugger off and leave them (I can hear some of my friends now saying I should) but no I do not. It's not all about how quickly you get there it is more about the journey.
So the 2nd bit of advice for group riding is, try to maintain your position in a group, If you are the 3rd 4th or 25th bike in a group, remain in your position as bikers passing each other in a group can be dangerous as we are all busy looking at those in front we are not expecting someone to pull off a quick overtake up the inside or outside, and if for some reason you have to move suddenly, you have arrived at the scene of the accident, and believe me I know how much it hurts to fall off a motorbike.
This being said if you do need to pass those in front do so, but remember plenty of room they may not be expecting it. Now something to consider is the size of the group. I have ridden with 2 motorbikes and also ridden with a couple of hundred.
When the group gets very large you may want to consider some of the following.
Does everybody know the route?
No? You may want to use the corner man system.
The lead rider will indicate where he want the following biker to stop at a junction to indicate to the rest of the group what direction you are turning at the lights/junction or roundabout. the "marker" will then wait for the Tail rider or rear gunner or whatever name you want to give to the guy at the back to catch up, then the marker may rejoin, usually in front of the tail rider. Once rejoined keep your position and eventually you will be behind the lead rider.
That brings us nicely to the tail rider, this can be anyone in the group, but if someone who has a distinctive motorbike or clothing (some groups use a different high viz for this rider) they can be useful, just make everyone aware who the tail rider is. Also the tail rider should be aware of the route you are taking and also have the number or means to contact the lead rider.
In very large groups you may sometimes get ride marshals, these will normally always be wearing high viz clothing and even have flashing amber lights to identify themselves, they may even be blood bikers but most certainly advanced bikers of some sort (ROPSA or IAM).
So I thought this was going to be a quick post but as it happens there is a lot to consider about group riding, and even more I have not yet covered.
I hope you enjoy reading this and I will post some more soon.