Ultimate Campaign on Companions on Controlling Companions includes the following:
How a companion works depends on the campaign as well as the companion's nature, intelligence, and abilities. In some cases, the rules do not specify whether you or the GM controls the companion. If you're entirely in control, the companion acts like a subsidiary PC, doing exactly what you want just like a true PC. If the GM is control, you can make suggestions or attempt to influence the companion, but the GM determines whether the creature is willing or able to attempt what you want. (140)
The section then describes the behavior of sentient companions:
A sentient companion (a creature that can understand language and has an Intelligence score of at least 3) is considered your ally and obeys your suggestions and orders to the best of its ability. It won't necessarily blindly follow a suicidal order, but it has your interests at heart and does what it can to keep you alive. Paladin bonded mounts, familiars, and cohorts fall into this category, and are usually player-controlled companions. (ibid.)
Emphasis mine. Hence, it's likely that even if the GM is controlling the imp familiar, while the wizard's imp familiar will probably not like the paladin, the imp familiar may nonetheless understand that keeping the paladin alive helps keep you alive, and will (somehow) attempt to heal the paladin on your behalf.