I am not English and not a teacher, but when you use 'older' is for comparing two things, like in your case.
You must use the superlative form in your example, because you are comparing Denise with the group composed by the two sisters. Among the both girls the more older is Denise, but she is the oldest of the group, do you follow me?
I am not English and not a teacher, but when you use 'older' is for comparing two things, like in your case.
You must use the superlative form ?? in your example, because you are comparing Denise with the group composed by the two sisters. Among the both girls the more older is Denise, but she is the oldest of the group, do you follow me?
The group for me is the two girls, but nonetheless, you are certainly right. Indeed it's not natural to say it in English (Im not sure I'm not English, you know).
Thanks for your answer, it is very useful. Now, I am not going to make the same mistake.
Cordially [A French guy who tries to learn English alone];-)