I can think of two ways. One is to have everyone connected, either physically (in the same room) or electronically, via e.g. Zoom, to execute their documents. A second way might be to have different people execute their documents on different days, and put them in escrow. When the last required deliverable has been received, there is an opening or "break" of the escrow.
Are these valid ways to achieve simultaneity, and are there "third" ways that I have missed?
When is this necessary, or at least advisable? Are these procedures mainly for contracts, or are there other uses for them?