What level are you?
Does Wynne have regeneration and group heal in addition to just heal?
Going with Wynne, Morrigan and Alistair as your companions, I'm gathering the top of the hill isn't a problem, it's down in front of the chantry. It's tricky and can require a lot of micro managaement and positioning, but it is doable.
To begin with, getting down the hill is the critical bit. If Wynne has Haste, then turn it on. It should stay on during the entire fight. It will likely slow down Alistair's and your attacks, but it will help you get your people into position faster. If Wynne does not have haste, then use speed potions before the messenger arrives to signal the scene change. These will help you get down hill faster, although they will wear off.
If Wynne has mass rejuvenation, that can be a winner right there. That will boost your stamina and Wynne's and Morrigan's mana. Cast it early and cast it often.
Put all the lyrium potions into Wynne and Morrigan's quickbars. There are four types, there should be four icons in their quickbars. This will allow you to have them drink them quickly as needed.
If Morrigan has any area of effect elemental spells, that can be handy. Have her cast one outside the barrier area on one of the skellies avenues of approach. One such area is the bridge, the other is the area off to the side. This will weaken the baddies as they come.
Have Morrigan cast the aoe debuff on one of the two elite skellies. She should cast the other on the other elite. Wynne should be set to [b]no[/no] combat. Alistair's tactics should be set to at health < 50% consume smallest health poultice. Next is shield wall, then threaten. He should bash any elites, then attack any. His stance should be aggressive. Do not attack the skellies yourself until either one aggros on Morrigan (drop him fast!) or Alistair engages the elites.
You will have to monitor the health of the villagers. If one drops below half, then have Wynne heal him. If one is an aggro magnet, but isn't below half (Murdock or Lloyd) then Wynne should cast regeneration on him. Use group heal for healing party members or yourself. There are certain narrow passages. Park Morrigan by one (I like the one nearest the bridge) and have her cone of cold any group of two or more. If cone of cold is on cooldown, then the other two cone attacks will do some good. Have Alistair use war cry, if he has it, on groups as well.
The one exception to Wynne not attacking is earthquake. It casts instantly, so use it on incoming groups of skellies that are still away from the villagers. This will help with crowd control.
As for your PC, use the multi target attacks, not the single attack ones. You want to attack and aggro as many as possible at once. The only two exceptions to this are the two elite skellies at the very beginning. Take them down ASAP.
Here is the wiki article on the subject
Best of luck!