Done it with 5, not too tough.
If you want to be cheap, hug the right side of the wall. You will avoid about 50ish of the monsters that dwell in that area since they all roam around the center path.
ALWAYS watch your radar, cannot stress that enough. Patrols have a tendency to stand still for an extended period of time but they will move if you walk into certain areas.
Someone with a longbow. There is one of the groups of shadows in the center that you'll need to pull out, unless you want to kill I believe it's two mobs of 2 hydras, 2 skales, and 1 smoke walker. The mesmer in that group tends to be reluctant in moving.
If you stand beside/behind the house at the back, the patrols will not come close enough to attack you. In fact, if you completely hug the right wall (all the way to the house) you will barely be able to pass by the patrols at the end. I haven't done the quest in a while but I'm fairly certain thats what we did when we had 5 members that one time.
Should you opt to completely clear the place (good idea, LOTS of drops), just take it slow. After you engage a patrol, another one will probably come so pull back if you need to. Again, just keep an eye on the radar and watch the patrol patterns for a while if you have to.
Key skills in this area: Maelstrom, Meteor, Meteor Shower, and pretty much anything else that can disrupt. Should the hydras get off meteor showers hope your tank is the target and that they have dolyak signet so they don't get knocked over. Try to get the smoke walker to stand by the hydras so that a single AoE interrupt will get all three. Convert Hexes also works very nicely on your tank since they will be hit with a Life Transfer and Life Siphon right away. It will help them take the damage from the hydras with some ease. Healing Seed and Mark of Protection are also both very nice for dealing with the hydra's Phoenix, Meteor Shower and Inferno.
If you have any crucial maintained enchantments, always watch your skillbar since the skales tend to toss around Rend Enchantments every now and then. This is the one area will you will regret not bringing in the outcast mesmers because every instance in which I had one when doing this quest it was quite easy.
Hope that helps.
