Thanks Amit and Wally for your valuable answers. That really helps.
So, now, If you can advise if this is correct :
1) Resepctive Service Groups Persistenly frozen on both the nodes since OS maintanace is being carried on both the nodes at the same time and both the nodes will require reboot.
2) Apps will be brought down manually.
3) OS maintanace starts for which I am going to move rc2.d and rc3.d scripts for VCS on both the nodes so that with every reboot I don't have to worry about the cluster part. I will be doing hastop -all before this.
4) Once OS patches are applied in Single user mode the scripts will be replaced so that with the reboot cluster comes up [with the same state as it was before doing hastop -all ? ? ? ]
5) Since the groups are frozen persistently, apps will be brough up maunally after which SG's will be unfreezed persistently.
Regards,
Saurabh