Not worth the effort to stick with old hardware, to be honest.
Just upgrade the CPU, RAM and go to an SSD, if it's all out of warranty. The speed boost will often cut hours off production regardless of software.
Software wise, try some of the old versions of
VSDC Video Editor
But if you have a good enough internet connection you can try the Cloud based options like Movie Maker Online. In fact if one of your family are in college/uni they can get Adobe Cloud Suite for a nominal fee.