Asking someone about someone else in your greetings

Question

Person 'X' and person 'Y' live together.

You bump into the person 'X' on street and what to ask the 'X' about the person 'Y'.

How would you ask informally how a person "Y's" life is going during your greeting?

I can think of four sentences, but I have no idea whether they all naturally and idiomatically work in this sense:

a. How's everything with 'Y'?
b. What's up with 'Y'?
c. How's it going with 'Y'?
d. How's 'Y' doing?

If no, then please let me know how they do not work and what is the best way to ask about such that thing?

Answer 1

a. How's everything with "Y"? -- perfectly grammatical and all right, nothing implied, allows the responder to choose whether to respond in detail, just in general, or with comments plus some evaluation of their own how much you want to know.

b. What's up with "Y"? -- This suggests that you know something about "Y" that you do not understand -- for example, they recently quit their job. It could just mean that you want to know how they're doing, but it suggests a little more than that. It is also decidedly less formal, as if you have a friendly relationship with "X".

c. How's it going with "Y"? -- Very much like option 'a', very slightly less formal.

d. How's "Y" doing? -- also similar to 'a', now that I consider it.

All of them are all right. Option 'b' could be slightly confusing to someone who heard the implication instead of just the query.