How can I calculate max, min frequency between FF to FF in RTL design?
As stated, there is no min frequency requirement. You can stop the clock and hold the present state.

The minimum period = 0.5ns output delay + 5 ns comb delay + 1 ns setup + 1 ns clock skew
 = 7.5 ns
So the maximum frequency limit is 1 / 7.5ns = 133MHz

With a clock skew of 1 ns, output hold time &lt; 0.5ns, the FF input hold time of 1 ns is not met from FF directly to FF. So that needs to be looked into. For FF--Comb--FF paths, the FF input hold time is met if comb delay has a minimum of 2ns.

New edit in response to below:

The spec that says clock skew is -1 or 0 ns is a little unusually stated, but it is reasonable to interpret that as overall clock skew being no more than 1ns.

Take an example of FF1--->FF2. We will take the clock fed to FF1 as reference. When the clock changes, the output of FF1 may change right away (i.e. 0ns delay, given there is no explicitly stated spec). Now assume the clock fed to FF2 is 1ns later (an 1ns clock skew). Then the output of FF1, which is the input of FF2, changes 1ns before the clock of FF2. Therefore, the actual input data hold time that FF2 sees is -1ns, and the spec is 1ns. So it is off by 2ns.

Now for FF1-->Comb-->FF2, if Comb can guarantee a minimum of 2ns delay, then the input data hold time of FF2 would be guaranteed to be satisfied.

The setup time is embedded in minimum period calculation above. Working backward:  

Setup time (min) = Clock period - Output delay - Combination logic delay - Clock skew