What should I do about my feeling that our maid has a relationship with the driver, after I saw her repeatedly opening the window and talking to him? And should I tell my family about this?

The family members must treat the maid as a stranger (non-mahram). Therefore, she should not uncover herself before the men of the household, nor should she be alone with any of them. Similarly, it is obligatory to prevent the driver from being alone with her. Lenient treatment in this regard is an objectionable act that leads to corruption. It is advisable to bring a maid accompanied by her mahram (unmarriageable kin) or a driver with his wife to avoid these corrupting influences.