Is the questioner sinful if he does not replace prayer rugs that have pictures of the Kaaba on them, and are the worshippers who step on those images while praying sinful?

There is no harm in your colleagues stepping on a depiction of the Kaaba drawn on a prayer rug. Entering the Kaaba and stepping on it with one's feet is not forbidden. However, it is preferable to pray on a rug that is free of images and patterns, based on the Hadith of Aisha, may Allah be pleased with her, that the Prophet, peace and blessings be upon him, prayed in a Khamisah (a striped garment) that had markings, and it distracted him from his prayer. This indicates the dislike of praying on patterned rugs and anything that might distract thewer. Therefore, there is no sin upon you if you abandon such rugs, and you are not obliged to replace them.