Why "duo pueri", but "duae feminae"? Do numerals change in Latin?
Yes and no, some are declined and some are not.
unus, una, unum for "one", duo, duae, duo for "two", and tres, tria for "three" are some that are declined.
quattuor ("four") and quinque ("five") are two that are indeclinable.
Only unus, duo, and tres, are declined, not >3
Multiples of hundred are also declined: ducenti, -ae, -a; trecenti, quadringenti etc.
"Domi duae feminae dormiunt" was marked wrong... is that an error?
No, in Latin they use the SOV sistem, so: "duae feminae"- subject, "domi"- object and "dormiunt"-verb, even though Latin being a flexible language, this is the most common way sentences appears
I am really glad there is a Duo Latin course. I hope it continues to develop. One thing that would be useful is to vary the vocabulary more. A few more verbs and nouns with the same grammar practice would be great, as they do in the Italian course,