The Kazlauskai surname spelling is the plural spelling of the Kazlauskas surname. Or it could be a corrupted spelling of the unmarried female spelling of Kazlauskas which would be Kazlauskaite.
The surname ending in Lithuanian changes for females depending upon their marital status. Mrs. Kazlauskas would be KAZLAUSKIENE (adding of the IENE ending).
For unmarried females, the endings are AITE (Kazlauskas becomes Kazlauskaite), YTE (Ralys becomes Ralyte) or UTE (Senkus becomes Senkute).