What is the difference between jsi and ty jsi
None. Because the verb gets conjugated to match the person that is acting it, you do not need to use personal pronoun. You can, you do not have to.
I am confused about the difference between, Jsi and Jste and when to use which.
I understand one is singular: You are (Ty jsi), and the other one is plural: You guys are (Vy jste)
Also, one is used as "Formal / Polite" (Jste) and "Informal / Familiar" (Jsi) - although these customs seem to be more and more relaxed these days.
Why is it Ty and not To. Is Ty both masculine and feminine? What am I missing here?
Here Ty = You.
Should "Jsi ty František" be accepted?
Not really, that is good for a question.
Are YOU Frantisek?
Jsi TY František?