Multi-property exchanges are rather complex, so professional guidance is recommended. A link to the Reg section appears below but it may not be of much help since some of the examples are no longer relevant after tax reform (personal property is used in some examples). Regardless, it would be wise to seek an in-person consultation with a tax professional who if familiar with, and has prepared returns for, multi-asset exchanges.
https://www.law.cornell.edu/cfr/text/26/1.1031(j)-1
