Most and lotsa are two different words with different meanings, so it is not possible to give antonyms for the phrase "most lotsa" as such.
Most means the majority or the greatest amount, while lotsa is a slang term for "a lot of" or "a large amount of." Instead, we can give antonyms for both words:
Antonyms for "most" could include least, fewest, minority, or some.
Antonyms for "lotsa" could include little, few, scarce, or a small amount.
Using these antonyms can help make your writing more precise and avoid confusion with the original meanings of the words.