I have a 16-year-old "step-nephew". He's never really felt like part of the family (neither do my brother and SIL's three kids, though), but is always at my mom's for the Christmas morning gift opening. DH & I always buy him a gift certificate for HMV. The reason he doesn't feel like part of the family has to do with family dynamics and has nothing to do with him. It would be hard on him to have to sit there and watch everybody else (the other 11 kids and three siblings with spouses, and mom and stepdad, and my stepbrother, and...my godmother, I guess you'd call her. I wouldn't do that to the guy. I think it's only fair to get him something. I think that applies to your step-sons, too.
Like the pp's, I can't imagine why they don't like the "goodie box". If someone gave ds1 (he's almost 13) a box of junk food as a gift, he'd be over the moon!
I agree with pp's about the Gameboys. I actualy hate the things. But, I think it's unreasonable to expect two teenage boys to have to socialize with people they don't well for an extended period of time. And, I don't think it will give them very pleasant Christmas memories, either. I'd agree - expect them to be polite and sociable for an hour or so, then they can go play their games somewhere else. (DS1 and my 10-year-old nephew always vanish into the TV room.)
Our family has the big gift opening at mom's place. The way it works for us is that we each open our gifts at home as a family (ie. me, dh & our kids at our house; my brother, SIL & their kids at their house and my sister, BIL & their kids at their house), then we all meet up at mom's at about 10:00 or so. We exchange all the "inter-family" gifts...the ones to and from the grandparents and between the grown-up siblings and the nieces and nephews. It's a chaotic hour or so, but everyone has fun...and we don't have any massive discrepancies in gifts to address. Would something like that work for your family?
I hope you can get this sorted out. I have a stepdad & stepbrother, and each of us has one child from a previous relationship, plus our current families and my brother has his stepson, and I have to co-ordinate with my ex's family and buy them gifts from ds1 (he has no money of his own, and my ex isn't even in the picture). The whole "step" thing gets awfully confusing at the holidays.
Oh...and I'd make a point of telling your mom, sister and everybody else that any gross infractions against common courtesy (eg. not apologizing, smearing food on the floor) on the part of your dss's should be brought to your attention immediately. I'm sure some of that is boredom at work, but it's not acceptable, and you can't be expected to deal with it if you don't know it's happening.