Possible silly suggestion. But perhaps do Newbury - Westbury - Waterloo?
There is a direct service to Waterloo from Westbury around 16:30 and you'll pick up a First Advance from
WSB» - Z123 for probably around ^20 each (Those a singles remember!)
However I second the suggestion of the drive to Basingstoke and train from there. Once at Waterloo it's straight onto the Jubilee Line and you'll arrive at North Greenwich in less than 10 minutes. (Any Stratford or West Ham bound service will call at North Greenwich). Returning back you may also be able to pick up a Southeastern Service from Greenwich National Rail station (Different from the
DLR▸ Station which is also different from North Greenwich; bear that in mind
) to Waterloo East from there it is about a 5 minute walk (all under canopy and easily found) into the main Waterloo Station
Alot of the
BSK▸ - WAT Trains are also direct so no changes necessarily and would most certainly be easier for an interchange into the Jubilee Line. Infact, a few of them are final call Waterloo.
However if your friends do go into Paddington. I recommend advising a change at Baker Street from either the Bakerloo, Circle, District or H&C Lines onto the Jubilee Line. It's a sod of a station mind, but for Jubilee line, it's probably the most sensible station to change at. Whilst you can interchange between Bakerloo and Jubilee also at Waterloo. From personal experience I would strongly discourage that. There is
ALOT of walking involved; especially if you're not familiar with the Underground part of Waterloo