The resorts you want to go to are pretty much all ace but I think for two weeks without your own transport it would be too much, you will spend too many days travelling. Better to stick to one area possibly.
You could ride for two weeks in Deuz alpes/Vaujany/Alp d’huez/Os en Oisans and if you got bored head back towards Grenoble and do a few days round Les 7 Laux and Chamrousse (close to the city)
You could go to the Tarentaise and ride Tigne/3 Vallees/Les arc (bit of a drag from grenoble though but there is a train to Bourg st Maurice at least). Tigne has free lifts so thats a winner 🙂
Alternatively you could fly to Turin and do the alpi bike parks (Sestriere/Bardonecchia/Sauze D’Olx and Montgenevre. There is a train from Turin to Bardonecchia for sure.
There is likely to be buses from bourg d’oisans to Briancon but I am not sure if they take bikes. And then you will need to get from Briancon to Montgenevre which is another 15k or so.
Edit: If it was me, I wouldnt do that road trip without my own transport.