Why cant you say hunder mine?
"Hundene mine" is fine.
It's always indefinite noun if the possessive is placed in front (mine hunder) and definite noun if the possessive in placed after (hundene mine).
Can someone help me with gode vs. godt, and god?
Adjectives are dependent on the noun. When plural (such as dogs), often the adjective has an e on the end.
En god hund. Mange gode hunder.
Neutral nouns often get a t on the end of the adjective.
En stort bord.
Why is "hundene mine er gode dyr" marked as wrong?
That's an accepted translation.
I think it wasn't when i tried it. But maybe i misspelled something and did not notice it. Thanks for your answer.