Drop the ーます from the ーます form and add なさい to make this form.
The Japanese translation is quite nice except the tense. 「…。」と、（先生は）指示しました／指示した。
In the English version of the first example, perhaps "just those" instead of "(just) people." Also, I don't know how they do it in schools abroad, but in Japan, the teacher normally says "should stand up" instead of "should sit down."
I guess this is half way between a 'polite command' and a 'fairly forceful request'.
[V-masu base] + nasai
'[The teacher]' isn't explicitly in the Japanese version, but the English might look odd without it.
'(just)' wouldn't be natural in the English - the だけ in the Japanese doesn't explicitly tranlate.
The coloring in ex #1248 is very confusing. The 'し' looks to be part of '早く', which is not the intention, if I understand correctly.