Just off phone with Delta as trying to see if there are spaces to use GUC on KLM marketed and operated flight.

The agent told me that:
1. They can not apply GUC to KLM flight as I bought ticket from KLM and it's operated by KLM as well. But the returning ticket(bought from KLM/AF as well) but operated by DELTA(so it shows in my delta app when I tried to assign my seat in AF.com, it brings me to delta app on my phone and I chose my seat) and she said they can apply GUC on the return flight. This seems to me does not make sense but what I was told for the KLM part.
2. I have 4 tickets on the same reservation so she said GUC will bump us from main only to comfort+, not to Premium economy. I thought it should upgrade us directly to PE then waitlist for delta one?

Anyone can share lights on this?