N.D.
I dont think the problem is as much about being a step mom as it is the fact he is 14. Google 14 y/o behavior and you will be surprised how they behave. here is one site.
http://www.cdc.gov/ncbddd/child/earlyadolescence.htm
His hormones are hormoning, he is feeling that he is grown-up and doesnt need to be told what to do. As far as his being fresh, depending on what he says it might not be fresh to his point of view, also his voice is changing and often what boys say at this age comes out sounding sassy, when its really their tone of voice.
If his parents have set the rules I would think its up to them to enforce them or at least enforce the consequences. At 14 he should be having less rules and restrictions rather than too many. If he is playing football for his school, his coach will have given him rules to go by, which include doing his homework. It might be time to let him decide some things himself and let him fail. I think a meeting with all four of you might help clear the air. Ask your SS what he wants and what he thinks his consequences should be for each infraction of rules. IE: Not doing a chore, perhaps an extra task, staying out late, earlier curfew, etc.
Above all TRY not to argue. I know this is hard, kids his age LOVE to argue, debate and in general upset the 'rents. Do not ask him a debatable question. Did you take out the garbage? when you know he didnt. Simply say please take out the garbage now, it stinks.
At other times it will do him good to get into a debate with you and it will bring you closer. Debate about the football game, politics, gas prices, stray dogs. Anything that isnt close to home, but gives you both some stimulating conversation. I used to disagree with my teens, just to hear their views, even if I agreed with them secretly. Then after they presented me with a good argument I could "see" their POV.