Background: Motion City Soundtrack was an American rock band that formed in Minneapolis, Minnesota in 1997. The band's line-up consisted of vocalist and guitarist Justin Pierre, lead guitarist Joshua Cain, keyboardist Jesse Johnson, bassist Matthew Taylor, and drummer Tony Thaxton.
Context: Motion City Soundtrack was formed in Minneapolis, Minnesota in 1997 by singer-songwriter Justin Pierre and guitarist Joshua Cain. Previously, the duo had separately played in a number of bands. Cain was in a group named the Saddest Girl Story, and recruited Pierre to join as a singer. He was subsequently in a band called Boxcar, and following its dissolution, he and Pierre founded Motion City Soundtrack together. The band's name was created by Cain's brother, Brian. Their early days were difficult, as they found it hard to break out of their local scene. When they could get weeks off from their jobs, they would tour. According to Cain, the members of the band soon realized that there "wasn't really anywhere to play [shows] in Minneapolis", and that they would have to "tour all the time" to rise in popularity. In its early years, the group went through several lineup changes. Through these, Cain and Pierre would often have to take over keyboard duties during shows. The group's first release was a 7" single, "Promenade / Carolina", released in 1999. Their next two releases, both extended plays--Kids for America and Back to the Beat--were released the following year.  Over the course of the early 2000s, the band continued to tour and shuffle through members. In late 2001, while touring in Milton, Pennsylvania with the band Submerge, they convinced two of its members--bassist Matthew Taylor and drummer Tony Thaxton--to join Motion City. Thaxton initially took about a year to convince to join the band. Jesse Johnson, a friend and co-worker of Cain's, joined the band as keyboardist just three weeks before the band recorded their first album. Johnson had never played the keyboard before but Cain taught him the parts that had already been written. After their first attempt at self-recording an album failed, the band culled together $6,000 to record with producer Ed Rose, best known for his work with the Get Up Kids. They recorded much of their debut album, I Am the Movie, in ten days. Initial copies were hand-packaged inside floppy disks, which were sold out of the back of their tour van for a year.  The band began receiving offers from various record labels, including Universal, Triple Crown Records, and Drive-Thru Records, and they performed at industry showcases. Meanwhile, Brett Gurewitz, founder of Epitaph Records, learned of the band from members of the group Matchbook Romance. He attended four of their shows in Los Angeles that Pierre later regarded as among his worst, as his voice was poor from constant touring. While they were interested in Universal, they chose to sign to Epitaph as they felt the contract was less restrictive and more honest. Eli Janney from Girls Against Boys helped the band secure management and a lawyer. Motion City became part of a slew of Epitaph signings, including Matchbook Romance, Scatter the Ashes and From First to Last, amid concerns the Southern California label had strayed too far from its roots, and seemed "a little too emo."
Question: How many members did they change?

Answer:
they convinced two of its members--bassist Matthew Taylor and drummer Tony Thaxton--to join Motion City.