---------- Post added 2012-12-17 at 12:46 PM ----------
I can't say the easiest way to do this with 5. 5 out of 10 or 15 people is a very low chance of being successful with achievements that need a planned strat that would require the majority of the team to participate. As many mentioned though, you could get lucky and face a horde team of brand new 90s, afkers, bots etc. 5 people against a horde random that's unified probably won't happen and you'll just have to keep trying.
I think it's more luck based then ever it was before since blizzard decided to remove all but a little bit of control for BGs. (By a little bit I mean they removed the ability to go with 10 or 15 and just made it 5). Previously you could counter all the unwanted random pug downfalls and increase your chances of success by a lot, whereas now you are at the mercy of 5, 10 or 35 potential idiots.