Here’s an example of a sentence I’ve come across — actually, part of a sentence. Is it necessary to use "who" a second time in the sentence, before "may" (see example below)? If not necessary, is it preferred to use "who" for each relative clause?
… for those who need access to these reports and papers, and may need more advanced resources.
… for those who need access to these reports and papers, and who may need more advanced resources.”
Either option is acceptable. There is a slight difference in how each of them may be read.
In the expanded option,
… for those
(1) who need access to these reports and papers, and
(2) who may need more advanced resources.
There is a slight tendency to read the repetition of relative clauses beginning with who as referring to two distinct subsets of the people you’re talking about, (1) and (2). Some people may need access to reports, some may need more advanced resources, and some may need both.
Compare to an elided version:
for those who
(1) need access to these reports and papers and
(2) may need more advanced resources
We’ve shifted from a compound relative clause starting with who to a compound predicate with one who as the subject. Yes, it’s also possible to read this as two relative clauses with an ellipsis omitting the second who, but there’s no guarantee people will read it that way. The result is that there is no clue whether the two statements refer to the same people or not. The group referred to by "who" is possibly homogenous.