Many properties allow you to pay for accommodation in installments rather than in a single lump sum payment. However, they will usually require you to have a UK-based guarantor (a resident of the United Kingdom between the age of 18 and 75 who will be able to pay your rent).
Yes, many student properties in Henley-on-Thames allow for dual occupancy of their rooms (e.g. for couples, best friends, siblings). Some properties offer this option absolutely for free, others charge a little extra. When browsing student rooms on Campusboard watch out for the 'Dual occupancy' label which will explain the terms for that room.