"certain" and "sure" mean the same thing, so you don't need to use both of them in the same sentence. Are you sure he's dead? -- is correct Are you certain he's dead? -- is correct I hope this helps :)

If you connect with the words "and" or "or". Yes it is OK "Are you certain and sure he's dead?" "Are you certain or sure he's dead?" You can also use this construct "Are you certain and/or sure he's dead?" = either certain and sure or either certain or sure. However although some speakers say things like this usually we use only one or the other. CERTAIN: adjective adjective: certain 1. able to be firmly relied on to happen or be the case. 2. specific but not explicitly named or stated. "he raised certain personal problems with me" SURE: adjective 1. completely confident that one is right. "I'm sure I've seen that dress before" 2. certain to receive, get, or do something. "United are sure of a UEFA Cup place" 3. true beyond any doubt. "what is sure is that learning is a complex business"

No there’s no need to use both. They mean the same thing so choose just one :)

Are you certain? Are you certain sure you're right?

Nope. They mean the same thing. Just use one of them