Question: Are Kai Hansen and Peter Steele both vocalists?

Context articles: Dark Assault
Helloween
Kids of the Century
Gamma Ray (band)
Blast from the Past (album)
Tiger (Frank Buck album)
Peter Steele
Kai Hansen
Keeper of the Seven Keys: Part I
Land of the Free (Gamma Ray album)

Dark Assault is the third studio album by the German power metal band Iron Savior.
 It continues the science fiction story that the band introduced on their debut album "Iron Savior" and continued on "Unification" and the "Interlude" EP.
 It is the first album to feature guitarist Joachim Küstner and the last to feature Kai Hansen before committing himself back to his band Gamma Ray.
Helloween is a German power metal band founded in 1984 in Hamburg, Northern Germany by members of bands Iron Fist and Gentry.
 Its first line-up consisted of singer and guitarist Kai Hansen, bass guitarist Markus Grosskopf, guitarist Michael Weikath, and drummer Ingo Schwichtenberg.
 After the release of a self-titled EP and their debut album "Walls of Jericho" in 1985, it expanded into a quintet with the addition of singer Michael Kiske, Hansen choosing to focus on guitar instead.
 Under this line-up, they released the "Keeper of the Seven Keys" albums (1987 and 1988), which established Helloween as a notable heavy metal band and led to the creation of the power metal subgenre.
 However, Hansen left the band quickly after the release of "Part II" and was replaced by Roland Grapow.
 He then created the band Gamma Ray.
"Kids of the Century" is a song and single by the German power metal band Helloween taken from the album "Pink Bubbles Go Ape".
 This is the first Helloween single with Roland Grapow playing guitars, replacing Kai Hansen.
 It is also the first Helloween recording with a song written by bassist Markus Grosskopf: "Shit and Lobster".
Gamma Ray is a power metal band from Hamburg, northern Germany, founded and fronted by Kai Hansen after his departure from the German power metal band Helloween.
 Hansen is the current lead vocalist, guitarist as well as the chief songwriter of Gamma Ray.
 The band is known as one of the most prominent bands of the German heavy metal scene.
Blast from the Past is a two CD compilation album that contains re-recordings of older Gamma Ray material from the Ralf Scheepers era, with Kai Hansen singing the vocals, and remasters of more recent tracks.
 All instruments for old songs were also re-recorded, with new arrangements, by the then current members of the band.
Tiger, a children’s record, was Frank Buck’s last recorded performance.
 The story was adapted by "Peter Steele" and Hecky Krasnow.
 In fact, Krasnow often wrote under two names, "Peter Steele" and "Hecky Krasno", dropping the "w." In "Tiger" Krasnow combined two animals from two stories in "Bring 'Em Back Alive":
Petrus Thomas Ratajczyk (January 4, 1962 – April 14, 2010), better known by his stage name Peter Steele, was the lead singer, bassist and composer for the gothic metal band Type O Negative.
 Before forming Type O Negative, he had created the metal group Fallout and the thrash band Carnivore.
Kai Michael Hansen (born 17 January 1963) is a heavy metal guitarist and vocalist.
Keeper of the Seven Keys: Part I is the second studio album by German power metal band Helloween, released in 1987.
 It marks the first appearance of vocalist Michael Kiske, and is considered the album that created the genre of European-style power metal.
 Kai Hansen stepped away from doing vocal duties as he had difficulties singing and playing the guitar at the same time during the previous tour.
 It was an album dominated by Hansen, due to an injury to co-guitarist Michael Weikath which prevented him from performing on much of the album. "
Future World" was released as a single and a music video was made for "Halloween" but with 8 minutes omitted from the song.
 The band originally planned to release "Keeper of the Seven Keys: Part I" and "" as a double album, but their record label refused, insisting that the albums be released separately.
 Much later in 2010, both albums were released together with bonus tracks.
Land of the Free is the fourth studio album by German power metal band Gamma Ray, released in 1995.
 Continuing a trend that would conclude with the band's fifth studio release, the lineup for the album was different from the previous one, as "Land of the Free" was the first Gamma Ray album to be released since the departure of Ralf Scheepers, leaving Kai Hansen to take up lead vocals.
 While not his first stint as a vocalist (Hansen had sung lead for Helloween until 1987 and had also recorded lead vocals on "Heal Me" from "Insanity and Genius"), it would be the first time he had performed lead vocals exclusively in 8 years.