Paris RER ticket good through Metro

From CDG, using a single RER ticket at 10.30€ allows you to connect to as many métro stations as you need to reach your final destination.

Les Halls is basically a métro line 4 stop which is physically located above and has access to the RER lines. Effectively, Châtelet/les Halls is really one big interconnected, underground station.

An RER ticket is good to any métro station in Paris. Does not matter where you change lines or how many times.
Make sure you follow signs "Correspondence" (=change), and not "Sortie" (=exit). You will go through one set of ticket barriers when you change from the RER to the métro, and a final one when you exit the métro at your final station ("Sortie"). After that your ticket is no longer valid.

Merci, we are leaving tomorrow and needed a few questions answered now as we have to meet with the landlord at 9 am sharp come thursday morning. Now, as long as the plane is on time at
6:30 am at CDG....:)

I wish you an on time flight, no waiting at baggage retrieval, and no queues at passport control.

Have a good time....

You never need your ticket to exit the metro -- there are no exit stiles. However you can be checked for a valid ticket so it is important to have it. Stiff on the spot fines for those who don't have their tickets.

You do exit RER stations through stiles, so for example at Gare du Nord you would exit through an RER stile since the ticket is metered and then re-insert it into the corresponding metro entrance. The machine will know you are on a single trip.

The 10.30 ticket from CDG to Paris takes you anywhere in Paris on RER/metro as long as you stay underground and do not exit (except for RER transfer as noted above); it works the same way in reverse, the ticket takes you from any metro station to CDG.

Question then, going through Les Halles to Chatelet i will have to exit RER then enter metro for line 7 or just continue through and use ticket to access line 7?

At Châtelet, just follow the signs to métro 7. Always keep your tickets until you exit the transportation network but effectively you will exit the RER perimeter and re-enter at turnstiles for métro 7.

Here is a plan of the underground spaghetti that is Chatelet-Les Halles station. In fact, the No 4 Metro line has 2 stations there, Chatelet and Les Halles.
https://en.wikipedia.org/wiki/Ch%C3%A2telet%E2%80%93Les_Halles#/media/File:Complexe_souterrain_Ch%C3%A2telet.svg