I find that very small numbers need more per sheep. Partly because the amount they waste is disproportionate, and also the scaling up thing (when feeding 20 people you end up with a lot left over if you multiply "enough for 2" by 10.)
Then I double it if they are going to be kept in and so get nothing from the grass.
Ex-BH's rule of thumb for commercial upland ewes out on grass was 20 sheep eat one small bale a day. (*) Mostly sheep aren't interested in hay until some point in December, and most years the grass is enough by about mid-March. But you don't want to be caught out if we have an early winter and/or a late spring, so budget for at least 4 months.
For 2 wethers I would probably get 20 bales in. You might have a bit left if the winter is mildish and short, but they can have that first next winter, or, if you don't want to do that, buy hay made from meadow grass not a rye-rich crop, and as long as you store it properly, you could sell any left over in spring for horses.
And then, when the time comes to be feeding it, give them a flap / slice in the morning, spread out along the ground (unless it is too windy), and have a look-see how much is left by early afternoon. If none, give them another slice in the evening. If some is left, no more till the next morning, and give them a bit less until they don't leave any.
When you spread it out, use a bit of fresh ground each time. They will waste more if they come to old hay or dung while they are eating

.
Or use a little hay rack or a sheep haynet. They do seem to waste more that way, but sometimes it can't be helped if it's too windy or the ground is really muddy so the outdoor spread-out way doesn't work.
Once they have learned to love their hay, you may find you don't need to spread it out, they will eat it off the slice. Then you can just put a slice down on the ground even if it's windy.
Come spring, rake up all the detritus as soon as you can; old hay left lying chokes the grass and eventually wrecks the soil's ability to drain.
(*) Our moorland Swaledales ate about half this much.