There area lot of things we don't know about here, so it won't be possible to provide you with a really accurate answer. (For example, we don't know the extent of the other guys' injuries, or weather a weapon was used to cause them. Further, we don't know whether your boyfriend's previous offences were for violence, or for other matters).
However, I'll try to provide you with a few pointers. Start by taking a look at the table on page 13 of this document:
http://www.sentencing-guidelines.gov.uk/docs/a ssault-against-the%20person.pdf
The sentences shown there are the ones which a judge must pass (other than under very exceptional circumstances) on a first-time offender, convicted for a single 'Section 18' offence, after a trial. Your boyfriend's previous record will push those sentences upwards, as will the fact that he's facing two charges on this occasion, but an early guilty plea could see any sentence cut by a third.
With the limited information available, my guess would be that your boyfriend might consider himself lucky to get a 6 year sentence. (If he did, he might be out in 3 years). However, if he's previously been convicted for offences of violence (especially if that was for GBH), there's a very high chance that he'll be given an IPP sentence. That's an 'indeterminate' sentence, for 'public protection'. It's effectively the same as a life sentence, in that the judge sets a minimum time which must be served in prison, but the offender won't be released until he's no longer regarded as posing a risk to society.
If your boyfriend is given an IPP, the 'tariff' might be for something like 7years. That would mean that he
might be released after 7 years but there could be no guarantee of it, and he could actually spend many more years in prison.
Chris