Whether an adverb can modify a noun (pronoun) or not has been debated and there is no firm conclusion. For example,
Almost (or Nearly) everybody came.
Some argue that here almost or nearly are adjectives modifying the pronoun everybody. Some also argue that they are adverbs modifying everybody. But, others argue they are adverbs that modify the determiner every rather than the pronoun everybody. Just because everybody is a one word doesn't mean they can't modify every. English parts of speech are not very clear cut and there could be more arguments based on how you analyze the parts of speech. Your examples:
I earn a lot more money than my sister does.
I have a lot more things in common with my friends than my family.
I can't stand much more things of this.
I eat a lot less things / food than I used to.
As you can see, if you insert appropriate words after the determiner more and less, they are not pronouns any more. They are determiners (adjectives). Also, you need to note that more and less could function as adverbs. Therefore, it is very hard to say they modify (pro)nouns.