In this sentences, both combinations are accepted in both languages. We usually want the learners to keep the order of words (like, not putting "dogs and cats" as an answer to "koty i psy"), but here... well, I guess this is not the most fortunate phrase to teach, actually. Well, not every exercise can be perfect.
English adjective order puts size before quality. "Big tasty sandwich" is correct English, "tasty big sandwich" is not generally correct English and, when translating from Polish to English, "tasty big sandwiches" needs to big accepted which it is not currently (as of 11/05/2018). I have reported this
It would be, but the phrase mentions plural sandwiches, not a singular one.
"Smaczne" is both neuter and not masculine-personal. So is "duże" (I assume you meant it). Neuter version is always the same as not masculine-personal. "Duzi" is actually masculine personal.
If you don't know it yet, plural in Polish divides into two options. "masculine personal" is for any group of people including at least one man. "not masculine-personal" is for anything else. So sandwiches as well.