The LHR-GRU in cheapest economy will only be 35 tps. Adding a Madrid leg would add 10 points - still short of your 80 point target.
If you can go more expensive economy (YBH fares), and go through Madrid you'd get enough at 70 for the long haul and 20 for the short haul flight.
Or WTP to GRU will give 90 points.

The other option is to go through the US eg LHR-JFK-MIA-GRU - at a discount economy fare this would yield 35+10+35 points.