Although I worked in information technology, I'm not an expert on scanners, but I'm not aware of double-sided scanning, but one thing you should be aware of, is that it is probably rather risky to put treasured family documents through a machine that involves them going through many rollers. I would imagine double-sided scanning is possible, but do be aware. Another thing I would say is that the resolution even on low end mobile phones is an alternative that you should think about. I often photograph a document, and use an online optical character recognition scanning service to extract the text. I think you can even do it with Google images on a phone or tablet.
Zaph