There are five tests that IRS uses to determine dependency status and all five tests have to be met.
1. Relationship/household member test.
2. Joint return test.
3.Citizenship test
4. Gross income test
5. Support test.
For all the F-1's that are not allowed to file joint return, test 2 will fail. The most debatable test is 3, citizenship test. According to Pub501, only US citizen, residence, and citizen from mexico and canada can be claimed as dependent. For the definition of residence, if you read carefully of Pub519, it must be permanent residence, not B visa, which means you can only claim a parent with GC status as dependent, then the rest of tests all have to be met first.
Remember, cheating in tax is a federal felony.