Firstly, are you really all that worried about trying to create studio quality lighting, in the stands at a ball park? I would think that as long as you can get a good exposure of your family, while at the same time getting a good exposure of the scene (field etc.), then that would be good enough. Basically, you would need to know how to balance your ambient exposure with your flash exposure.
That has nothing to do with flash accessories, and everything to do with knowing how to do it with your camera & flash settings.
Secondly, if you do want to worry about the quality of light (not just the quantity), then you would want to make it soft and directional. To soften light, you need to make the light source significantly larger, relative to the subject (larger and/or closer). If you look at the Lightsphere, or Flip-it or even a small softbox....do they really make the light all that much bigger? Maybe a little bit, but unless you are making your light at least 12-16 inches wide/tall, then I don't think you would see much difference at all. Especially when you're far enough away to get a few people in the shot.
This is the big fallacy with flash accessories. So many people think they are making their flashed light better, simply by putting some sort of hat on their flash....or by tilting the flash and shooting it off of a card etc. But what you (and so many others) need to realize, is that simply doing that won't really help at all. 80% of flash accessories are really only helpful when you are bouncing the light off of walls or ceilings anyway. And if that is the case, you can often just bounce the bare flash, and get pretty good results...much better than direct flash.
I'm not saying that most accessories don't help...but most of them require that you use them in rather specific situations. Of course, they don't tell you that...they want you to think that they work great anytime...and judging by what I see people writing and saying...they (the flash accessory marketing union) are convincing a lot of people.
So my advice, would be (if you won't be satisfied with simply balancing the flash & ambient), to find a wall somewhere and bounce the flash into that. Position your family in a spot that is close to the wall, but that allows for the background that you want. It may not be easy to do...in which case, it may not be worth the trouble to bounce, just shoot direct but get the balance right.