I think they have to ease out of the rough housing activities - not just because of their size differences, but because it's not appropriate anymore, at least not outside of the wrestling ring. They both need to find other ways of engaging with a member of the opposite sex without physical play. I realize there's nothing sexual going on between them, but they need to both model different behaviors within their peer group, and learning to have discussions or trade good-natured verbal barbs is a life skill they both need. If his hormones haven't fully kicked in, then it's all the more important that you work on these skills before he's through puberty. And your daughter is going to discover that, while she may be able to physically dominate her brother, she's in no way equipped to defend herself against a more powerful high school boy who has the height and weight advantage that her brother does not.
We often think of girls having body image problems, and your situation reminds us that boys do too. We place so much emphasis on looks, strength, agility, and more - and they get it from every media outlet and every social interaction as well as every sports hero. It may help to show him successful men who have not ever gotten as tall as they might have hoped, but who do just fine when paired with a taller woman. I was doing dishes the other night while "Dancing With the Starts" was on, and host Erin Andrews is quite a bit taller than host Tom Bergeron as well as several of the dancers. In fact, some of the pro dancers are quite short. Ryan Seacrest is noticeably shorter than his girlfriend but he's had no trouble being successful. Michael J. Fox is admired in many ways and has been for 30 years. There are pro basketball players who are not at all tall - although if your son is not into sports, maybe you don't want to push those images on him. Maybe he needs help seeing that sports isn't the only field available to him. I'm sure you can come up with dozens of examples of people who were not defined by their biology.
And maybe your daughter needs more work in being sensitive to others. It's an acquired skill, certainly - but it's a good time for her to see that her attitude is going to give her fewer friends in high school. I'm not singling her out - I think this is common in most 14 year olds. She's got the body of a woman but the viewpoint of a kid, and the next few years need to be spent on bringing those more into line.
There's no way to know if your son is done growing or if he'll get a spurt at 17 or 18. So it's important for both of them to work on identifying WHY our society puts so much focus on bodies, and whether that's a good thing. What can each of them do to be more compassionate to people with different body types? How fortunate are they that they have the use of both legs and arms? Who's around them who has far more challenges? You can expand that during dinner table discussions to include those of different skin colors, religions, economic standings, and so on - disadvantages come in all categories.