I went through the screen shots you provided another time and put together the file sizes. You are right, it's risky to run the "Delete All". According to the screen shots you may need something in between 450 and 600GB of temporary additional disk space.
Your current options are:
- take the risk (I would NOT do it)
- rebuild the .vmsd file and delete the snapshots 1-by-1 (latest vmware.log file required)
- increase the datastore to 1.99TB (not more!) which will give you the additional free disk space you need
- clone the second disk to another datastore with sufficient free disk space.
André