Can anyone give me advice on what my friends may get for a section 18 offence or GBH?

My friends have told me they are innocent, to be honest i believe them i'd like to find out what sort of sentence they are looking at if they are found guilty though (but lets hope they're not). They were supposedly stood outside a teenagers house, the teenager ran out with weapons and started towards my friends, one of then then apparently hit him with a beer bottle which was left at the scene, the other two, i'm told, joined in and hit and kicked the teenager. He sustained some injuries of which included cuts where he needed stitches, bruises and broken ribs. there are apparently three witnesses, one of which was the beaten up teenager, the others are an OAP relative and a close friend, will the witnesses relation to the teenager make any difference in court? also the teenager and his friends knew the attackers names but the elderly relative doesn't but could easily have been shown photos via Facebook/Myspace et, the witnesses have to point out the boys on video line up, if they know them is there any point in this? if so please can you clarify? , what could be the reason for this because the names were given on the same night of the incident. i believe they have the beer bottle but they have said possible fingerprints were found, if they had there fingerprints wouldn't this be enough for a guilty verdict straight away? or are the police allowed to pretend they have the bottle to get a confession? and if they do have the bottle and the prints at the scene could they say it may have been put there by someone else if it has someone else's prints on it as well? since this was a while ago and they denied the offence they stated they could not remember where they were on the night, they also said the usual thing to do on that night was go to town drinking, the place where the incident happened is far away from where they said they were, if they cannot prove they were there can they give a guilty verdict? They have no previous for violent offences and they are all over 18, also what would they be looking at if they were under 18? Finally is there a certain amount of evidence they need to compile to prosecute? The three all have very good solicitors and straight stories. any answers at all would be a great help, but please don't comment if you're just going to moan about what they supposedly did, thanks a lot James.