I need to get from CDG to near Metro-Boissiere at around 10pm on a Friday and then back at 5am in the morning on a Sunday, how would I do this?
Take the RER B train from CDG to Paris until Denfert-Rochereau station. Transfer (using same ticket) to Metro line 6 direction Charles-de-Gaulle-Etoile until Boissiere station. Trains run up until midnight from CDG so you shouldn't have any issues.
On the way back to CDG you'll need to take a night bus as the first Metro trains start running at 5:40 am from Boissiere. If it's OK to arrive at CDG around 6:30AM just reverse your route: Metro line 6 direction Nation until Denfert-Rochereau, transfer to RER B direction Aeroport CDG 1 or 2.
If you need to arrive at CDG earlier, say 5:40AM, you can catch a Noctilien (Night) bus 143 from Gare de l'Est to CDG Terminal 3 at 4:45AM from Gare de l'Est. Best to take an Uber or taxi from Boissiere to Gare de 'lEst as night buses would require 3 transfers.