Double relative clause

In a sentences like this:

I know people who are good at this and who can help you.

I can drop either the second who or and the sentence will still be ok and make sense. I can't drop them both though. I'm pretty sure about it. Correct me if I'm wrong

What I'm not sure about is this kind of sentence because we've got 2 kinds of relative clauses

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

Does it sound ok and correct?

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.

You have a couple of options for making this both correct and more fluent. A key concept here is the possibility of using the word "they" to refer back to an entity that you have previously mentioned.

Option 1 Use "they" to replace the second "who".

I know people who are good at this and they can help you.

Option 2 Split your compound sentence into two separate sentences.

I know people who are good at this. They can help you.

Option 3 Use a comma or a semi-colon.

I know people who are good at this, and who can help you.

Your second sentence is all kind of mixed up. I think one major problem is that you're getting stuck on inserting 'i know them!' into your sentence.

I can name a few people who got a job in that company.

Or:

I have a few friends who got jobs in that company.

To be grammatically correct, your sentence #2 would need to read something like:

I can name a few people, with whom I am friends, who got jobs in that company.

It may be my personal opinion, but the re-write makes you sound like an arrogant jerk. Sorry.