It all depends on the mount system(s) of the lenses. If you know what camera they went on when you bought them, that can help you get there, otherwise, you may have to try and resort to more difficult means, like this visual guide to dSLR lens mounts.
The six mounts that can easily be adapted to Canon dSLRs with simple adapter rings are:
- Leica R
- Nikon F
- Olympus OM
- M42 (aka Pentax thread/screw mount)
- Pentax K
Note how Canon FD/FL or Minolta MD/MC are not on that list. Other SLR mounts are liable to have a smaller registration distance than Canon EOS mount, and will require an optical element in the adapter to act like a short teleconverter, which will compromise image quality to a certain degree.
Be aware you won't have nearly the same features/function as with a native-mount current lens. No autofocus, no wide-open metering, no modes that require the camera to adjust the aperture of the lens, no lens EXIF, etc. See also: Can I use lens brand X on interchangeable lens camera brand Y?).
Macro reversal rings
With macro reversal rings, it's much easier. Because you're mounting the lens backwards by its filter threads, you just need to know the individual filter sizes of the lenses, and then get the appropriate sized male-to-male rings (if you're reversing the lens by mounting it face-to-face on another lens). Or you can get a reverse-mount ring (EOS mount on one side, filter threads on the other), and then appropriate step-up/step-down rings to get everything to fit.
To find the filter size, look on the front of the ring for the diameter symbol (⌀), and the size next to it is the filter size of the lens (e.g., "⌀67" means the lens takes a 67mm filter).