Hi @sumarao9: When you say 2 different versions of PEGA to be merged to single 8.x instance, basically you are trying to merge 2 code base / 2 DB into single code version / DB. What I would suggest is either of the below.

• Upgrade one of the application to the latest version of PEGA first and deploy the other code base to the latest 8.x version.
• Upgrade both versions to 8 and do a code sync

Few impacted areas which you need to be careful:

• Conflicts to be verified between both versions of your source in terms of organization category rules and data, classes, rulesets, access rights of users
• OOTB table overrides to be verified
• DSS and other data instance conflicts

As a alternate, check if process fabric can solve your problem of merging.

Also please refer: https://support.pega.com/question/merge-two-different-pega-instances-one-instance

Thanks.