You failed.Marth uthrow chaingrabs fox and falco until 60-low70%, where he finishes it off with a tippered fsmash. There may certain precise ranges where fox and falco can DI up and shine marth before they can grab. If someone could clear this up and give exact %'s, that'd be amazing.
I believe fox can get out of marth's cg at very early percentages(I did it at 0-5% or so) if marth doesn't pivot grab, if he does he can cg fox up to 80% or so and kill with pivot tipper, etc. but most marths will prefer to combo you out of his cg with uptilts or double fairs, or ken combo,meh.. lame and cheap stuff(expect that at 40% or so), same goes for falco(I guess).