Learn English – When do you leave out the preposition in a relative clause

There is a complication in using multiple relative clauses that is semantic rather than syntactic in nature. Your first example involves serial, coordinated relative clauses. I've chosen examples I prefer to work with:

*/? I know some people who work with toddlers and who like grapefruit.

I'd say this pairing of clauses would in most contexts be too semantically disparate to work.

I know some people who work with toddlers and who attend karate classes.

This works better, the contrast being acceptable. These are {people who both work with toddlers and attend karate classes}

I know some people who work in computing and who could [therefore] probably help you.

Here, the second clause follows on naturally from the first. If the optional therefore is included, the first clause is of course non-optional.

In the following examples, the serial clauses would not work:

*There are a few people who/m I've met and who know all about the dextroboper problem. [and who like grapefruit ...]

It doesn't make sense to serialise such disparate statements

There are a few people, who/m I've met, who know all about the dextroboper problem.

ie there are only {a few who know all about the problem}, and I've met them all: 'who I've met' is a parenthetical

There are a few people who/m I've met who know all about the dextroboper problem.

ie amongst {the people I've met}, a few know all about the problem.

Looking at your second sentence,

I can name a few people who I'm friends with and who got a job in that company.

is again a coordination.

I can name a few people [who I'm friends with] [and] [who got a job in that company].

But in your

I can name a few people who I'm friends with who got a job in that company.

there is not coordination, but sub-setting (nesting of clauses):

I can name [a few people who I'm friends with {who got a job in that company}].

cf

I can name [some friends {who got a job in that company}].

The 'who' can't be dropped in 'standard British English' in the first of these two sentences, and dropping it in the second sounds like an informal AmE usage.

Whether a relative clause is defining or non-defining (some writers say integrated or supplementary) is really more about semantics than punctuation. The first relative clause in the Original Poster's example is probably just an unconventionally punctuated non-defining relative clause. The clause neither explains which money it was that was given nor is an integral feature of the money that was given. Rather, it is a supplementary story about what happened to the money after it was given. (However, see further below)

The Original Poster's feelings about sentence (3) are actually the feelings that we should have about sentence (1). If this was actually a defining relative clause it might give us the uneasy impression that the money was already spent at the time of giving.

The rules for the omission of a relative pronoun can be summarised as follows:

1. The clause will usually be a defining relative clause.
2. The pronoun may not be the subject of the main clause in the relative clause (in technical terms it may not be the subject of the matrix clause in the RC).
3. The relative pronoun may not be the complement of a preposition in a fronted prepositional phrase.

The second rule there means that it is not important whether the word is the object of the clause or not. The only thing that is important is that it isn't the subject of the main verb in the clause. To illustrate the point, the pronoun may well be the subject of a subordinate clause within the relative clause:

• That is the man [who] we suspect took the money.

In the relative clause above, who represents the subject of the subordinate clause:

• [He] took the money.

The Original Poster's Questions

We can, of course, say (1). However, we would need a special reason to present the relative clause as a defining relative clause. We need some reason for which she spent immediately to be an integral part of the money. Here's a contrived example:

A: People never spend the money you give them immediately.

B: Rubbish! I gave Jane some money she spent immediately.

We could of course say money which she spent immediately and include the relative pronoun. This sentence does not quite have the same meaning as the Original Poster's number (3). The reason for this is that this sentence presents the fact that the money was spent immediately as an integral feature of the money for the purposes of the conversation.