When would be the best time to worm them? It's not very often they all come up to the house.. I have a few that like to hang out in the nature conservancy that surrounds us. Once the weather warms up we don't see them too much, all the hens stay close and a few of cocks, what I think are the younger males tend to wonder. I can hear them out there when they call each other....
We recommend a spring and fall worming, some people say every 3 months, but I think that is more suitable for southern states where internal parasites are active all year round. The spring worming is considered important for getting the birds in top condition for the rigors of egg laying, the fall worming will give them a chance to put on the weight and fat they need to survive the cold winters. Keep in mind with a free range bunch like yours they have likely not been wormed for years. Many would wonder why they survive okay without it, and the answer is that any wild ranging animal will have a "worm load" if they are otherwise healthy their body can deal with a certain parasite population, and even keep it in check. This is not so much the case with the young ones, and may be why you had those winter losses. However, if the birds become sick with something else or injured, a worm load can quickly get out of hand and kill them, so we worm to give them that extra boost against the parasites.