Hello,
I specialize in developing indicators and EAs for MT4, and have completed 150+ MT4 projects here with excellent ratings.
I read your requirements, and although all open positions cannot be closed in one sweep, they can be closed in the same tick (with possiblity of a minor difference due to spread).
So, if there are 10 buy and 5 sell positions open, and we need to close them in one short, those 15 positions can be closed on the same tick. Each position is closed individually, but all positions can be closed on the same tick.
Looking forward to work with you,
Adi