Pronunciation question, please help?

Hi, no, they aren't.

English has two ways of pronouncing 's', a strong one /s/ and a weaker one /z/. Most words only have one of these two forms, but some can change form according to their position in the sentence.

For this kind of problems, you really need to consult a dictionary and have an idea of how the phonetic alphabet is read. Here are the entries of your words from an online dictionary:

AS ~ weak form /əz/ strong form /æz/
THIS ~ /ðɪs/
THESE ~ /ðiːz/
IS ~ strong form /ɪz/weak form /z/, /s/
Mary's ~ /-s/, /-z/

The sentence makes no sense to me, but it would be:

aZZ thisSS iZZ theeZZ Mary'ZZ

's always sounds like |z|

as, is and these are always pronounced like |z|

this is always like |s|