Can Composer XE 2016 FORTRAN and Composer XE 2017 FORTRAN coexist together? Currently I am using XE 2016 with VS 2013 and VS 2015 and contemplating to install Composer XE 2017 FORTRAN. However, it is essential Composer XE 2016 FORTRAN be still functional on the system.
That depends on what "coexist" means. I have IPS 2015, 2016 and 2017 on a laptop, and use the compiler from a console most of the time, using Visual Studio only when using the symbolic debugger. No problems at all.
If you require full integration with VS, the range of different compilers versions that can be selected (within the settings of a project) is a little bit narrower.