As mentioned this deal is available throughout whole year 2015 with no further restrictions. Max stay in Brazil 3 months. All these European cities are easy to reach either by bus or low cost airlines. To check your connection possibilities from your home town directly you may check through Skyscanner. Cheap accommodation in Sao Paulo is possible to compare and book here.
Booking samples
NL - Amsterdam - Sao Paulo - London for €429 (+€22 booking fee)
NL - Brussels - Sao Paulo - London for €431 (+€22 booking fee)
EN - Amsterdam - Sao Paulo - London for Ł326
EN - Brussels - Sao Paulo - London for Ł328
DE - Amsterdam - Sao Paulo - Frankfurt for €463
DE - Brussels - Sao Paulo - Frankfurt for €466
Booking sample of cheap open jaw flights Benelux - Sao Paulo - London/Frankfurt for Ł326 here. In this case you would be flying from Amsterdam to Sao Paulo on 7th of July and returning from Brazil back to London on 24th of July 2015.