Maybe, but they are autonomous enough (since 2009) that if they choose they can become completely independent. As in independent of Denmark. If they can become completely independent of Denmark then they can also be persuaded to join the United States or enter some kind of alliance. It’s entirely up to the people of Greenland.
Sounds like the Russian-speaking half of Ukraine!
You are correct.
Denmark has no say in this
They could be persuaded to join the USA, but then the question of Puerto Rico will also be brought up and we also have to reckon with the fact that Greenland has nationalized health care that works pretty well
None of it is insurmountable, but it's not easy either.

Under the later Tsars, from 1870 onwards AND during the Soviet period there was extensive Russification, i.e. the banning of local language (the French also did this using the Parisian dialect in France, killing off Occitan, Garcon, etc. etc. and the English did this using the Midlands dialect over York, Sussex etc.)
It is a simplification to say "they spoke Russian so are to be subjects of the Russian federation" - Zelenskyy is also a native Russian speaker, that was his first language and there are many like him and many Ukrainians whose parents were from what is now the Russian Federation.
Note that all Scots and nearly all Irish speak English exclusively - and the vast majorities of native Scots and native Irish can't speak their native languages, but does that make them English?