Help, PhD 'interview'

[MyUsernameDoesntHaveNumbers]

Have set up a new profile as want to keep this separate to my other posts on everyday life.
I am currently undertaking a full time MSc and thinking of a PhD. I have enquired about 2 PhDs and have been invited to meet with both supervisors on one and to 'lunch and meet the team' with the other. Both at different institutions.
My 'problem' is that I have no idea what to expect. Is this what usually happens with PhDs? Do they not have 'formal interviews?' Should I take it that both institutions are interested in me?
I Realise that I am essentially asking how long is a piece of string!

when I get enquiries from a sensible sounding PhD student, I normally set up an informal interview (on skype or real life) to decide if this is someone I can support for a PhD application. this means (a) is this person smart enough & motivated enough (b) does this person's desired project match my lab's work.

if this interview shows a good match between the candidate and supervisor (me), then I will support the student through the official university interview process and various funding applications. there are formal interviews in those later stages.

if the student is not a good match for the lab, I'll try to point them in the direction of a lab that might be right for them.

So this initial informal meeting is a bit like online dating - the student & supervisor have to get on well and agree on a PhD topic etc. Then the formal stuff can happen later.

Thanks Parietal.
Both PhDs have already got funding and projects are already sorted. I have emailed the supervisors a few times with questions and they to me so hope that this means that they already think that I might be a good bet.
Thanks for your help