Kaiser picked the Terps over Indiana and Virginia. He will play his senior season of high school basketball at IMG Academy.
The forward and center add to the Terps' frontcourt depth and take up their last two scholarship spots.
Carey averaged 13.5 points per game for the Hoyas last season.
Young averaged 19.6 points per game for Charlotte last season and will become the first DeMatha product to commit to the Terps in 20 years.
Amid coaching and roster changes, the Terps struggled to adapt and deliver.
Willard becomes the 10th head coach in Terp history.
Ayala and Russell combined for 37 points in their final outing as Terps.
With the loss, the Terps finish the season with a losing record for the first time since 1993.
The majority of the current Terps — including interim head coach Danny Manning — had never competed in the Big Ten before this season.
Despite Russell and Ayala being honorable mentions, no Terp was named to any of the all-Big Ten teams for the second straight season.