the trick to edge guarding yoshi is releasing that you can't hit him out of his jump but he really has no way to approach the stage. wait for the super armor to end, wait for watever attack/airdodge he does, and you hit him off stage and he has 0% chance of coming back.
ness's double jump is basically as good, minus the super armor, but he has the option of falling back and upbing (which is actually a good recovery if they dont jump out and get hit by the upb purposefully) if they simply defend the edge from your jump/airdodge/attack.
as far as djc, ness's is superior to yoshi's simply because yoshi has to wait an extra 5+ frames to do his 2nd jump or else he will just dj back into the ground. and ness's uair is vastly superior in terms of hitbox size, speed and combo uses (though yoshi's does kill better). Ness has an aerial kill move (bair) which yoshi doesn have, both nairs are pretty solid though i think yoshi's is a bit better overall. ness's fair is better for spacing and speed while yoshis combos better.
I think ness is a little better than yoshi because of these differences.