Build a latrine like the “survivors” in your back yard and “vote off ” anyone who doesn’t use it. Seriously if you have two or more bathrooms designate one as a main bathroom, which will leave one of them near perfect and easier to tidy quickly when the “In laws” arrive un-expectedly.
Convince the male members of the family to sit down when using the facilities. This is more readily accomplished by placing the latest issue of MAXIM magazine near the toilet for them to “read”, or by installing a television. This alone makes the bathroom much more sanitary and easy to keep clean. If he must stand, encourage your weekend warrior to install a urinal in the bath room, after all he should be using the right tool for the right job.
The best advice is to keep a mini cleaning kit under the sink. Buy a mini spray bottle and have a general-purpose window cleaner and a few good terry cleaning towels. Using one of your towels folded into quarters, polish the mirror after a quick spray of window cleaner. Give the chrome, sink and counter a quick spray, flip the towel to a clean dry side, and wipe it down, then flip the towel again, and polish to a brilliant shine. Flip your towel to another dry clean side and spray the toilet seat and rim. Wipe and polish dry the seat, under the seat and rim. Flip the towel to another clean dry surface and you can use the spray and towel to spot clean the floor.
The key is a good cleaning towel with lots of surface area to soak up and collect the general-purpose cleaner, hair, dust and dirt. Theroretically, when the towel is folded in quarters, you have 8 different cleaning surfaces. Do this often as an interim cleaning and a major cleaning and disinfecting of the bathroom is easy as pie.