I can't remember if Emma Samms and Catherine Oxenberg were on Dynasty at the same time. I think they might have been on one or two shows together.
It's interesting that Amanda and Fallon Carrington are in this movie together titled Treacherous Beauties.
Seems like they overlapped in 1984 to 1985, and had some time together at the show. Catherine Oxenberg left in 1985, and Emma Samms started playing her role in 1984. However I cannot remember if they were in scenes at the same time.
"Be the change you want to see in the world." M. Ghandi