Almost there. I mean, native speakers of Brazilian Portuguese tend to (or indiscriminately) use the verbs "is" and "isn't" and their corresponding past tenses "was" and "wasn't", "were" and "weren't" at the end of their question tags. They will also mix the tenses, but most of all they will use an "isn't" at the end. Like this:
"Your sister will come pick you up here,
isn't?" (instead of ", won't she?")
"The rocked failed to take off,
wasn't?" (instead of ", didn't it?")
"Bob and Jack haven't discussed it yet,
isn't?" (instead of ", have they?")
"Will they go?
is?" (instead of "Won't they?"
It appears to me then that my fellow countrymen do not seem to know which correct question tag goes at the end either in speech or in writing.