If Co-Signers Cannot Be in the Same Location, Can They Each Sign Separate Documents Individually?

Generally, there is no legal requirement that all signatures must appear on the same document, but that is assuming some key points.

First, it is obvious that each party signs a counterpart that contains the exact same language as the documents signed by all the others.

Also, be advised that when multiple copies are signed, it is usually appropriate to include language in the document indicating that multiple counterparts can be signed and each shall be treated as an original and the different counterparts treated as one agreement.