Question about HD upgrade

With all the info about the 5 lnb dish,I have a question that I'm not sure how to handle.I currently have 2 dishes set up,one on the side of my home and the other on the roof in back. the mother in law stays in back.when i first subscribe to dtv the installer didn't want to run cable all around the house so for a nominal fee he set up a second dish.at the time it seemed reasonable, he said the signal would degrade and i would lose picture quality.My question is if i upgrade the first dish to Hd.Can I still use the second dish for the mother in law or when you upgrade to Hd does your programing come from different satellites.will i need to change both dishes and boxes.I'm not to worried about her watching hd she's doesn't understand all the fuss.I just want her to be able to watch her soaps and the locals news as she does currently