To answer your first question, no, holding a Macho Brace will not double EVs gained from Super Training. The game treats Super Training and Horde Training, etc. as two entirely different methods of doing the same thing, and thus Macho and Power Items do not increase Super Training EVs.
I can't quite understand the second question, but I'll answer on the premise that you're asking if the affects of the Mach Brace/Power Item will be passed to your whole team while using the Exp. Share. The answer to that is no, they will not receive the benefits of the item. A word for the wise; when the Exp. Share is turned on, the other Pokémon in the party will receive the same EVs as the lead Pokémon in battle (before the boosting effect of the Macho Brace/Power Item).
For example, say I have a Tangrowth in the lead and a Starly and Mawile in my party, with the Exp. Share turned on. Tangrowth is holding a Macho Brace. He defeats a wild Shuppet, with an EV yield of 1 Attack.
will get 2 Atk EVs (Macho Brace)
and will get 1 Atk EV each (no Macho Brace)
So if you have a whole team of Pokémon to EV train, don't turn on the Exp. Share. You will find yourself using a lot more Berries and Reset Bags than you'd like.