You have to do the best you can with what you have and the ideal isnt always achievable.
So,
if you worm and keep them in as you have they shed what burden they had indoors. If they then go on to pasture which has been free of sheep for a good period ( 6 months is good ) then the idea is that any worms in the pasture will have died.
If you cant do that, and it isnt always possible. Then they are likely to pick up worms from the pasture and need worming again at an appropriate interval. I dont know if Alpacas have the same worms as sheep but cows, pigs chickens etc do not so you can clean a pasture by grazing animals that will digest the sheep worms but that are not a suitable host for that type of worm.
What we are all aiming for is a system of rotation which dramatically reduces the worm burned and eliminates the need for a frequent worming programme and avoids althalmic resistance.
Perhaps thats something you could aim for next year as it sounds like you just have too many balls to juggle right now.
And yes it's ok for Mrs Manx to play out in sight of her Manx friends.