The key is making sure that you have sufficient recovery time for the first race. Whenever I have raced half marathons 2 weeks apart I have had a couple of days recocery, then easy runs from Wedensday to Wednesday. Ater that Take it easy from Thursday until race day. Hope this helps.
you don't need a special app. A Google+ account allows you to see the location of people in your circles, if they allow it. My wife finds it very useful to use when I do races, allowing her to go for a coffe and return to the finish just in time to meet me as I cross the line.