"Hähnchensandwich" has "ein" because it is neuter. If it were masculine it would be "einen"
And the "ein" is taken from the sandwich (part of the word), that makes me wonder if composed words take their gender from the last component of it.
Very good observation. Most often, this is absolutely appropriate. For example: Die Schule, der Schultisch; der Abend, das Abendessen. The first word is often used like an adjective in these compositions, 'die Riesenfreude' = a huge joy, but gender and article relate to the word's base, which is in most cases the last component. There might be exceptions I'm not aware of right now though.
That would be "Sie essen ein Hähnchensandwich." You have to memorize the verb.
actually ihr esst
to sum it up
sie isst=she eats du isst= you eat (singular, informal) ihr esst=you eat (plural) Sie essen=you eat (formal)
When speaking/listening German, is there a clear difference between isst and ist in pronunciation? I'm even getting confused even when it's written down...
I would also like to know the difference in the pronunciation of isst and ist?
There is (in my experience) very little difference in the pronunciation. Technically you should be able to hear the extra 's' in 'isst' (i.e you would stretch the 's' slightly), but the native speakers I talk to are prone to speaking quickly and it is almost impossible to hear the difference. Context is very important in these cases.