We have multiple products. All can be installed separate but also installed at the same time. All are send as single MSI file. The issue is now the upgrade. If someone get a new MSI for one product it must fit at least to the major version of all other installed products.
The test with different upgrade code fails because if all are installed and each has the rule to allow the updates only within the same major version you can Deinstall one product and than install any version because there is no crosscheck