By making a call to a module from a module, you are required to include those subsequent called modules in any bind you request. This can be done in several ways, depending on what you want/need. You can bind them directly to the program of MODA (MODULE parm on CRTPGM command), or you can include then in a service program and reference the service program in the compile of MODA into a *PGM (BNDSRVPGM parm of the CRTPGM command)
When you use a service program, they are bound to the MODA *PGM by reference, when you bind them into the MODA *PGM directly, they are bound by copy.
As a guideline, I would suggest you bind a module to one-and-only-one object, (*SRVPGM or *PGM). That way, you only have to manage the one version. If it is bound in multiple locations, changes to that module will be more difficult to manage.