Question 1) Yes you can. However take care about following information:
You need different WebCenter DB schemas (WEBCENTER, ACTIVITIES, MDS) for each managed server.
Quesiton 2) Yes.
You're R1 will be in WC_CustomPortal1 that have following DataSources associated (WEBCENTERDS1, ACTIVITIESD1, MDSDS1).
You're R1 will be in WC_CustomPortal2 that have following DataSources associated (WEBCENTERDS2, ACTIVITIESD2, MDSDS2).
About the context-root you should change it. You can't have an application with the same context-root in the same WebLogic domain.
My recommendation: Have two different WebLogic Domains to maintain R1 and R2 in separate environments. Evolve R1 and R2 separately and apply versions to your applications.