If you moved into a 4-bed, then you two paying half would be fair (and your housemates' 50% share would be a greater amount than a 50% share on a 3-bed). If they only pay half, then they're getting 2 rooms for the price of 1.5 - you're getting 1 room for the price of 1.5.
Obviously, the flat isn't just 3 bedrooms: there are shared areas. Split the rent in half - one half for rooms, the other for shared areas. You two pay half share of the shared areas rent, and 1/3rd for the rooms proportion. Bills should probably be split equally.
Obviously, the flat isn't just 3 bedrooms: there are shared areas. Split the rent in half - one half for rooms, the other for shared areas. You two pay half share of the shared areas rent, and 1/3rd for the rooms proportion. Bills should probably be split equally.