The deinstallation of Oracle GI could be not so easy thing to do, because it contains many components one should be aware of. The proper deinstall is important because it will safe you from many issues with next install on these servers
In general we need to be sure that:
1. all sowftware stopped properly
2. removed from oraInventory
3. binaries removed
4. /etc/oracle cleared
5. ocr and votes cleared using dd
6. /etc/oratab updated
7. .profile updated
8. init.d files in /etc/ cleard
Usually its recommended to use deconfigure scripts, if they fails for some reason, the manual procedure should be followed.
How to Deconfigure/Reconfigure(Rebuild OCR) or Deinstall Grid Infrastructure [ID 1377349.1]
How to Deinstall Oracle Clusterware Home Manually [ID 1364419.1]
As general recommendation its good idea to save your crs configuration for future reference.