"There are flies in those sandals."
Translation:Tem moscas nessas sandálias.
I am not sure about this, and I didn't really say it MUST be 'têm', just that I think it's not necessarily wrong.
My point is merely that 'haver' is not really conjugated (as you point out), and I think this is because the verb doesn't need a preceding pronoun. (In English you would change from "there is" to "there are" to describe something existing in plural.)
'Ter', on the other hand, takes a pronoun (i.e. something/someone is having, even if we skip the pronoun in colloquial language). Therefore, you might ask "who or what has flies in it/them", and the answer would be the sandals in plural. Hence I thought it would be correct to use the plural form of 'ter' if this verb is chosen...
Don't know if this analysis makes any sense, and independent of this, I do agree that using 'haver' would be more correc/less colloquial slang, and it would also save us for the dilemma of conjugating 'ter'.
Applying English reasoning to Portuguese is often treacherous, alfsagen. :)
You see, it is not like "there are" and "there is" at all, because in English it is the verb "to be" that is used, not "to have" like in Portuguese. You could say "Essas sandálias têm moscas." Or in typical Duolingo weirdness: "Essas moscas têm sandálias." But if you put "Tem" in the beginning like that, the structure of the sentence makes it impossible for "moscas" or "sandálias" to be the subject. In this case, "ter" is used exactly like "haver" and is invariable.
Wouldn't be surprised if "haver" disappeared from modern Portuguese altogether if people start thinking "ter" can do it all.
Strictly "este" (i.e. 'nestas') means these whereas "esse" (i.e. 'nessas') means those. I'm working from the Android app at the moment, hence cannot provide a link, but several persons, among them myself, have already written about this other places. Short recap:
'Este aqui' --> means --> "This one here" 'Esse aí' --> means --> "That one there, where you are" (used to point at something close to the person you speak to, e.g. if he/she is holding something in their hands, if something is at an armlength distance from him/her or if you are speaking to someone on tje phone, and you want to discuss something where he/she lives, e.g. the weather where he/she lives as opposed to the weather at your own end. 'Aquele alí" (or 'aquele lá') --> means --> "That one there" (far from both yourself and the person you speak to).
In colloquial pt_BR the meaning of "esse" is less strict, it seems from previous discussions, and the word can be both "this" and "that".