[مستر وليد السيد]

Sender Atef Ahmed teacher

In Michael Swan's Practical English Usage, seventeenth impression 1989 page 144 (comparatives and Superlatives), I read the following:
The comparative is used to compare things or people that are separate from each other. The superlative is used to compare one member of a group with the whole group (including that member). Mary's nicer than her sisters. Mary's the nicest of the four girls in the family. In the first sentence, Mary is not one of the three sisters; we use the comparative. In the second sentence, Mary is one of the four girls that we are talking about; we use the superlative.
Isn’t our sentence similar to the second one here regardless of the number of people compared with? I’m sorry for my persistence.
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Editor's reply:

The sentence first asked about is simiilar except that there are only two people in the group. This is a point of grammar on which there is disagreement and, as I said in my first reply, I don't know which way the examiners will go on this, so it is best to teach the students to be conservative on this point, i.e. to use the comparative when only two things or people are being compared.
In Practical English Usage, 3rd ed. (2005), page 116, Swan says:
When a group only has two members, we sometimes use a comparative instead of a superlative.

I like Betty and Maud, but I think Maud's the nicer/nicest of the two.
I'll give you the bigger/biggest steak;: I'm not very hungry.

Some people feel that a superlative is incorrect in this case.