The Sage is willing to believe many things, but these Seekers may be beyond the Pale.
1. The Sage recognizes your dilemma. Your choices are to continue with a poor housekeeper; to try a new, random housekeeper; or to trust a friend to attempt the job and augment their income, at least on a trial basis. By all means, tell your friends that you don't trust them to do a good job, ask a fair price, or leave your private belongings alone. Then, when they cease to be friends, they should be happy to work as unfriendly housekeepers for even less. Even a one month trial might be enough to make them think you care, so carefully avoid it.
2. The Sage no longer is surprised by who steals what from common refrigerators. Executives usually don't get to their positions by acting fairly or nicely to those equal to or beneath them professionally. Unless the culprit is called out in the act or a security camera is placed in front of the refrigerator, there is no way to accuse anyone and have it turn out well, particularly not someone in a position to terminate the accuser. The Sage, therefore, prefers the bait-and-hitch method of catching food thieves. Leave something in the refrigerator, commenting in ths person's presence how delicious it is, which leaves a non-toxic but embarassing surprise, such as a laxative or bright ink which will be noticeable on the culprit's mouth after the meal.
3. The Sage recognizes your terror in this issue, that you might actually come into contact with someone's germ, which you could so easily hide from it it came in the form of a sudden sneeze, If you have children over the age of 6, post one of them by the restroom in your home to stop each offender coming out of the bathroom without washing to request they complete the task. Be certain to post public health posters about the proper method of washing, usually reserved for food service employees. At work is trickier; perhaps you can borrow the previous Seeker's security camera after her thief has been exposed. How you might use this camera to suitably embarasser the unwashed masses without exposing yourself as the source of the pictures is up to you.
4. The Sage strongly urges you to show your schizophrenic brother your great trust of him. Have him help you polish the knives in your home or clean any weapons, and then ask. Certainly he will be amused at your distrust of him, given the strong lack of any evidence of evil-doing. I certain he would be more than happy to confess to this and many other crimes when confronted like this. With luck, he might even return to his previous state of madness, triggered by your question.