Sorry about the very delayed reply.
Thank you for the suggestions on routes, I'll take a look at those It's reassuring to know we're not completely alone in our mistakes!
We probably couldn't afford a course, and wouldn't be able to do it anyway - my husband has a sleeping condition which, to cut a long explanation short, means getting to places at specific dates/times isn't possible. However, a friend has very kindly offered to take us up Moel Siabod and teach us some navigation skills, which we're going to take them up on
Mike - Regarding water, it probably doesn't sound too bad, but bearing in mind my pack weighed 18-20kg setting off and about 8kg of that was water, then my husband was carrying a similar amount... We're thinking it might be a good idea to get a water filter for next time.
Visibility was fine. The long grasses were a bit of an issue at times, though. As for where we got lost, it's hard to say. There is a point at which we think we should have crossed a stream but didn't, then we came back down again, crossed the stream/river but missed the path again. We basically started off trying to follow the stream the whole way up, having misunderstood the article with the route.
Post edited at 14:53