IMO an 8' wide bedroom is not ideal but for a twin bed it should work Are all the windows egress ones . I think if you need 3 bedrooms then this will have to work as long as egress is good and claset space is good go for it.

How about turning your two story foyer into a small bedroom by putting in a floor and a wall? If you can put a closet over the stairs and close in the stairs you may gain a smallish but a bedroom none the less. If you do a split with the larger bedroom you will need two new windows because they have to be egress windows and that wall maybe load bearing so you may not be able to move it. Maybe it is time to check with an engineer first.