So me and a friend of mine are playing talisman. We had a disagreement about evading on the crown of command. So me and him are on the crown dueling. we both are on one life. It is his turn and he dicides to cast invisablity on himself. He declares that he evades me. He decides to roll for command and rolls a 5.

Is this legal in the standard rules for talisman 4th ed. revised?

He's wrong. When two (or more) characters are on the CoC at the same time, they'll only encounter another character. To cast the Command Spell you'd need to encounter the space, but can't since another character is there. Evade is part of the combat sequence resolution, but to evade, you have to have first initiated your encounter with another character (though could use a special ability instead of choosing to battle/psychic combat).