to get tung cung mrt station by boat from island and fare of the taxi from mui wo.

It is impossible, but you can find ferry from Central Piers to reach Tung Chung directly.
From the Central to Tung Chung New Development Ferry Pier, it takes about 40 to 50 minutes on the way and the fare is 18HK$.
After you reach that pier, you can walk to reach Tung Chung MTR Station easily.
I am not very clear about the taxi fare, because I seldom take taxi in HK. From Mui Wo to Tung Chung Station, you can take bus 3M.