My sister does 'media free' chunks of time with her boys of similar ages. Which means that every so often, when the requests for tv/video games become a problem, she just tells them "this has now become a problem for me (as opposed to something they are managing on their own") and just puts away the wii, unplugs the tv and keeps it off during the daytime.
She's done this quite a few times (esp. in summer, when they put the wii away for sometimes a month or more) and says that after a few days, they do go out and play, they do find their own entertainment.
It sounds to me like your kids are a bit dependent on this form of engagement; perhaps it's time for yours to go away for a while, too.
As for the friend's house-- you can only control what goes on in your house, period. However, you are the parent and can limit how often/for how long your eldest gets to go off to friends. Homework has to be done first, etc.
Would you consider finding another, family-friendly activity? Picking up a few new board games (even from a thrift shop) for them to learn? Or what about geocaching. (If you have a GPS, Tampa may have a Geocaching website.)
My only tip from my house... let them keep busy in other ways. I have a found objects drawer my son pulls from to make creations. (He'll be 6 in April.) We make sure that we go out each day as a family (or the two of us) to get some exercise-- I often have to initiate this, but it's worth it. I also don't have the tv on myself during the day-- so a lot of this is modeling, myself, what's important to us. We choose to spend time at the library, out and about with friends, on nature walks or at the park, and I regularly grab Kiddo up to help me make dinner. I know this will change a bit has he gets older, but I feel like kids still need a lot of 'leading' from us in how they use their time.