Axle u-joints are tough to do, especially if they're old. There are ways to make it easier, but it's hard to describe in writing. Typical tools are a vice, some sockets (used as punches), and a 5lb mini-sledge. Your other option is to use a press tool, like a balljoint remover/installer.
It may be worth your while to take them to a place like Driveline Services and pay a few bucks each to have the guy there do them for you...
Chris