If you didn’t want to start a rift, you should have left the term “Modern Orthodox” out of it. It could have been asked as a general question. I know plenty of people who would probably be identified as Modern Orthodox who are makpid on these areas of halacha.
Not covering hair is clearly problematic mid’Oraisa, although I think some try to rationalize it by saying it stops being an ervah when it becomes normal in society for women to keep their hair uncovered. The Aruch Hashulchan says this regarding saying Krias Shema, but doesn’t seem to hold that it applies to the actualy uncovering of the hair.
Although most contemporary poskim do seem to asser pants, I don’t know of earlier sources to prohibit. Maybe some never accepted it as assur. Before asking for a source that it’s muttar, do you know the sources that it’s assur?