to open or close "simultaneously" on MT4 platform is not possible.
You can only open/close a position ONE at a time.
Opening multiple charts to run a "closer" script will cause "Context Busy" error which will put your account ON-HOLD for 30~60 seconds!!!
To close positions is to close ONE-AT-A-TIME..
When you say, "close multiple positions" are you referring to ALL positions of the same currency pair? or close ALL POSITIONS on ALL currency pairs?
Attached is a script a friend wrote for me:
You can select to
YES = Close ALL positions on ALL pairs
NO = Close ALL positions on current currency
Cancel = Do nothing
(This is a script NOT EA, save it inside EXPERTS/SCRIPT)