We're planning to upgrade our current backup exec version of BE2010 and BE2012 to BE 20.3 version. But I have read it from the forum that direct upgrade is not supported in our current backup software environment. As per the forum, we have to upgrade it first to BE2014 then to BE 20.3. But our concern is, do we still need to buy licenses for both BE2014 / BE20.3 so we could do in-place upgrade or buy the renewal support maintenance instead?
You should be able to install (upgrade) in trialware against the intermediate version (just don't enter a license during the upgrade).
You should probably review the infornation in https://www.veritas.com/content/support/en_US/article.100044372.html
Especially the information on compatibility and best practices.