No, the grandfather would be the least skilled of the three.

The basic idea is that to make a good archer, you need to start when he's (women need not apply) practically a baby. In order to teach well, you must be an archer yourself; thus, the father should be an archer.

Adding in the grandfather was probably a case of exaggeration for effect, but - no, I haven't read any diaries about it, so I could be wrong. You'd probably get some benefit from it.. I have no idea how much.