Exactly how do brokers work?

suppose this is in the context of commodity futures

customer X wants to do 100 lots ASAP, but sees B/A at 5/6 lots on the screen. So he calls up Brokers A, B, C.

Does X

1) divide up the orders across A, B, C 

2) he only uses 1 Broker at a time (ie: calls up A for 100 lots, first come, first all filled basis?)

3) Let all the brokers know he is looking for 100 lots, A/B/C comes up with their best fill/price and lets customer X choose among the 3 choices

Do brokers call up market makers (prop firms), banks, other parties to work together 100 lots or at once?

Once 100 lots is filled, does this show up in the "volume" metric on a charting platform? would this be a block trade?