1. can we watch two different shows on two different devices at the same time. will that work from one slingbox or will i need it on two tv's at home?
No, you would need two Slingboxes. Each Slingbox can view only one video source at a time and can only be viewed by one person. Not sure what you mean by needing 2 TVs ? TVs have nothing to do with the Slingbox. If you mean 2 TV 'sources' (Cable, OTA, Satellite) then the answer is yes,
2. if we want to stream to our televisons, is it easy? don't like watching tv on mobile devices.
You need a second box. Sling used to produce something called a Slingcatcher that allowed this, but it was discontinued. Although you might still find one on E-Bay. The WDTV box is the other option I am aware of, although people on this forum seem to be having trouble with it. if you have a laptop with an HDMI out plug that would also work.
3. says you can watch recorded tv. can you modify your recordings?
This is nothing to do with the Slingbox, it is down to your AV Device. Basically, you can do anything with the virtual remote that appears on your laptop/PC screen that you can do sitting in front of your AV device with the 'real' remote. This is what I see on my laptop when viewing my UK Sky box.
So I can do anything.