grammar - Parsing the sentence "the number of people..."

Here's a sentence I randomly thought of:

The number of people [who/that] don't give way to buses is staggering.

This sentence got me thinking about grammar and sentence structure and thus prompted this question. There are two parts to my question, which somewhat go together.

The first part is this: is "who" or "that" correct? I was fairly sure of "who", but then I thought, maybe it depends on how the first part of the sentence is parsed. Again, I'm fairly sure that #1 is correct; if it is, I'd also like to know whether #2 is plausible.

1. (The number of) people who...

In #1, people are the focus, so "who" is used.

2. The number (of people) that...

In #2, the number is the focus, so "that" is used (because the number is a concept).

This leads me to the second part of the question. What is the structure of the sentence? Below is what I think it is:

[The number of people] subject who [don't] verb [give way to] verb [buses] object [is staggering] phrase

(Is this also a clause on its own? Or is it a clause + a phrase?)

Now, if my breakdown of the sentence is correct, and the number of people is a compound subject, does that mean that (1) the first part of this question is moot, and (2) The number of people that doesn't is correct, despite linguistic norms?

In summary:

• Is "who" or "that" correct? Why?


• Have I analysed the sentence correctly?


• Is the number of people a compound subject? If so, why don't we say the number of people that doesn't?


• Is the entire sentence a clause, a clause + a phrase, or multiple clauses?