Never met a goose that didn't like lettuce. The hissing might be because they are still new and confused. Give it time, and by time I mean it could take months. You also will be coming up on breeding season in a few months and he will be particularly unpleasant then. But remember that you are the alpha at all times and let him know that. Do not show any fear because he will never forget that if you do. He may never be really friendly to you since he is mostly an adult when you got him. But with time and patience he will become more tolerant of you and your presence.So...we tried lettuce a couple of days ago hoping that if they like it then we could use it to lure them into their house of an evening, i'm not sure what to make of the outcome, they appeared to love it, we threw small pieces of it to them and they ate it without a second thought and ran for other bits that we threw to them, I couldn't quite believe how keen they were, the Gander then started hissing at us, he's never done this before and it seemed a bit weird, do they his if excited? or is he getting angry because we're not feeding him quickly enough? confused!!
We couldn't lure them into their house with it though, they still don't like the sawdust I think after three days they still don't want to go in at night and had to resort to using poles to guide them but it took some effort again, we put some lettuce in with them overnight but it was still there this morning only adding to the confusion.
When you say sawdust do you mean sawdust like what drops to the floor when you cut/saw wood? If so you might have bedding that is too fine for them and gets in their nostrils. Try to find either shavings (the large ones not the really fine ones) or even straw. If you use straw try to keep it as try as you can and replace it often. Wet straw is/can be a bacteria farm and that is really unhealthy for geese and ducks. I use straw but I stir it daily and replace it about every week for my three.