Just to makes things clear, there is no 50D mk II. There is a 50D and there is a 5D (series). So there is the original 5D, the 5D mark II and the 5D mark III (current).
The 5D series of cameras are what we call 'full frame'. That means they have a larger sensor that what is in your cameras. This has many advantages, but you should note that full frame cameras are only compatible with EF Canon lenses, and not EF-S Canon lenses.
So if you do upgrade to a full frame camera, you might need to replace your EF-S lenses (or just keep them with the Rebel cameras and get new lenses for the 5D).
Other upgrade options for you might be the T3i or the T4i. These would most closely match the cameras you have now.
You might look at a used 40D, 50D or a new 60D. These are a 'step up' in the Canon food chain. They are bigger & more robust. They have different ergonomics (better IMO).
The next step up would be the 7D. This camera has the most advanced auto focus system that you will find in a Canon camera that costs less than $3500. So for shooting action/sports, this would be a good choice.
All of the cameras mentioned above, would be compatible with your EF-S lenses...so that would be a benefit.
However, if you want to take your equipment (and maybe your business) to the next level...it might be worth jumping up to a full frame camera like the 5D mkII or 5D mkIII.....along with high quality lenses.
On the other hand, if you just upgraded your current lenses, and kept your current cameras...that might be enough of an upgrade for you...for the time being.