Multisite or several individual WordPress instalations

Hello,
till now I had experience with single, basic wordpress instalation and single domains.
This is the situation I have now, and I am looking for your advice about should I use WordPress Multisite:
– my clients already have their site up and running, let’s say their domain is client.com
– their main site is more less basic: slider or two on main page, news, basic info, several usual subpages, contact
-but they have several other websites, they currently “stand alone” ( separate hosting, some are subdomains like something.client.com some have their own domains webpage2.org ..), but since those organisations are under the main institution (client.com) they would like to integrate those separate websites into a portal which will work like this:
– on the main site we can see the recent news from all those separate pages
– all the separate pages/organizations will maintain and update their sites for themselves

I still don’t know if they plan to turn all of them into subdomains or keep current domains. They have a big mess there with permalinks and everything so I think that even maintaining google ranking is not important. We can build it from scratch and it would be better then it is now.

Do I even have to ask or the WordPress Multisite is the solution?

I don’t have experience with multisite so here are my questions- things I am mostly worried about:

1. in a multisite install, is it possible that one page, lest say
page1.client.com can run with wordpress theme Theme1, other one (page2.client.com) using another different Theme2 while the main site is on Theme0

2. since those separate sites now exist on different servers/(hosting),
can they stay that way in WordPress Multisite instalation or do I have to tell them they have to choose one hosting and server?

3. if they decide to have separate wordpress instalation for all the sites(this last question is in case they do not want to use Multisite) ,
is it possible to “pull” the recent news from all of them and display them on main site client.com ? (maybe to point me to right plugins…)-they have at least 5 separate websites which I will have to pull recent news from

I will be thankful for any advice you can give from your experience.
Thank you so much.