How to cite the same author multiples times in IEEE style?
In the IEEE style, and more generally in numeric citation styles, one only rarely writes the author names.
I'd thus rewrite the first sentence as

According to [5] [...]

Starting a sentence with a citation may not be inappropriate but may reduce readability (this kind of issues if frequently fixed by the copy editor anyway). I'd thus rewrite your second sentence as

In [5] it is argued that [...]