모두 다 이것은 원해요

Duolingo translates this as "Everybody wants this"
->모두 다 이것을 원해요. (strained expression)// 모두가 이것을 원해요 (more natural)
Google translates this as "This is all I want"
->이것 모두 다 원해요 (strained) // 나는 모두 다 원해요 (more natural)
Are these both correct? This is very confusing for an English speaker!

Both are incorrect.

모두 다 / 이것은 / 원해요

모두 다 =can be ' everyone ', and also can be 'everything'

이것은 = this (subjective)

원해요 = wants / want *Objective*

 in this sentence, there is '-은' in 이것은. '-은/는' is significative of Subjective. (but not only '은/는' and also '-이/가' can express subjective)

Example) 나는 학생이다(I am student) / 그는 학교에 간다 (He goes to school)

그가 지불했다. (He paid) / 노인이 쓰러졌다. (an old man fell down)

-모두 다

 -> in case which you express this for Subjective -> +은/는 or +이/가

example) 모두가 울었다(everyone cried) / 모든 사람은 일 해야 한다(every people should work)

 -> in case which you express this for Objective -> +을/를

example) 모두를 기쁘게 해주고 싶다(I want to make everyone happy)

in korean, 은/는, 이/가, 을/를 are often omited. but it would be better to express at least one of them to avoid confusion(BUT sometimes it sould be not sufficient to express by one of them. so the best choice is express every of them)