Videomaker – Learn video production and editing, camera reviews › Forums › Cameras and Camcorders › Professional Camcorders › Creating High Quality Edited Home Videos › Well, since you asked for
Well, since you asked for 'any' advice…
If you can get a 15 minute documetary for $1,500 do that!
I would advise against used cameras and especially cameras less than 1080 in resolution. Twins studies are of interest to a lot of researchers so keep the quality as high as possible because, of any home video project, yours may develop interest beyond your family.
Get an easy to use HD camcorder that has an external mic input and keep it handy. Just about any software is better than WMM. I'm an Adobe user, upgraded from Corel when I needed more flexibilty and speed. Others seem to like Vegas and if you use a Mac, FCP is the 'go to' product. If the idea is to really get into it, get one of the more professional NLE's.