Charizard takes fifty percent damage from the move, and Thundy takes 25%. Ouch
Although it doesn't like taking Focus Blast or HP Ground, Heatran can completely wall Charizard and the specially defensive set handles both Pokemon well, and doesn't mind being paralyzed
The scarf set can outspeed them both and ko with stone edge. It can remove the dangerous sun and rain both sweepers use to their advantage, and although it hates focus blast, but it can even take an LO Focus Blast from Thundy-I with assault vest and sand up.
Both dragons have no issue taking powerful electric and fire moves thanks to their high special defenses. Just watch out for dragon pulse from Charizard and a boosted HP Ice or dark pulse from Thundurus, and neither like paralysis.