It is the correct pronunciation.
singular male = דוב (dov)
singular female = דובה (duba)
plural male = דובים (dubim)
plural female = דובות (dubot)
It's not an uncommon phenomenon, that when the vowel turns from 'o' to 'u', the following consonant gets a dagesh. Another example - yellow is צהוב (tzahov) for singular masculine, but צהובה (tzehuba) for singular feminine. A drum is תוף (tof), but the plural is תופים (tupim).
Unfortunately not. /tsahov -> tsehubim, dov -> dubim/ vs. /qarov -> krovim, tov -> tovim/. I'm not sure what the linguists know about it, but I won't be surprised if in the ancient, pre-biblical history of the words, the singular of "yellow" and "bear" (but not of "close" and "good") was with /b/, too, and then it was reduced to /v/ when at the end of the word.
Well, it is not unusual in books for the youth, after they are weaned of complete niqqud, to resolve some ambiguities. In the first chapter of a random book of this kind I find in the first chapter גזֵרה (to read edict, not she cut), תִקווה (to read hope, not she will hope) and הַבטחָתי (to read my promise, not I promised). Duolingo does the same sometimes, pointing here to the fact, that the female הַדֻּבָּה needs a feminine verb. Niqqud is not a question of all or nothing and even in pointed texts the fullest form of Niqqud with every Dagesh and so on possible is seldom used.
Not just in books for the youth, most books have some words with some nikkud; I just checked the first book I saw (To Kill a Mockingbird) and I found, for example, אִתה ("with her" rather than "you"), יוּאל (Ewell, to distinguish from יוֹאֵל=Joel) and קלפּורניה (Calpurnia) every time her name appears.