Suppose I got a specialist but I didn't hire him, is it possible that I hire the next specialist and immediately promote him since I have one unhired previous specialist?

Correct me if I'm wrong, but I think you are asking if you decide NOT to hire a specialist if you can hire a specialist from the "next hire" option? You can't do what I just described. You have to use either hire from your current set of three options, or promote to get a new set of three.

What you CAN do is wait until you have the ability to hire two specialists and hire one and instantly promote it if it's from "current hires" section.

Welcome to the forums!

for example I have 3 hire options now which are infiltrator, Princess and martyr, bt I don't want any of these...so my next hire options are navigator,thief and saboteur....my question is, when the time reaches can I hire a navigator and instantly promote him to admiral since I haven't hired any of my previous options?

No can not. You have to either hire from your current set or promote a specialist to be able to hire the nav you want

Thank you so much