how many units in this building? where are you located.
what you describe sounds like a multi=family building with older plumbing and some issues.
1. There should be no single handle faucets anywhere in the building (one handle for hot and cold mixing) - cross over from hot to cold (evidenced by the hot water in the toilet) is a bad thing.
2. Failure to have anti-syphon protections, i.e. toilet tank fill valves, sprayers at kitchen sinks, etc.
3. Failure to have a pressure balancing or anti-scald protection in the bath/shower areas AND delivery of hot water at fixtures at scalding temperatures.
4. Booster and pressure controls between units either on the same riser or throughout the entire building plumbing system. Example, you are using water in your living unit, your neighbor elsewhere also draws water - your flow is interupted: sort of like in a single family home Dad is in the shower, and Mom sneaks in the bathroom and flushes the toilet - the sudden draw of cold water to rinse and re-fill the toilet tank causes Dad to get scalded in the shower.
Depending on the age of the building, its history, the location, the number of living units, etc. will determine how much of this will/might be required to be corrected (plumbing system, grandfather clauses, etc.). If you reside under a rental contract versus a purchased co-op or condo unit might determine additional resources/agencies that you could elicit enforcement assistance and advice (for example if rental unit - some sort of rental unit licensing inspection, complaint unit, etc.). Plumbing violations for multi-tenancy or multi family units might be addressed or inspected by your local public health department, etc.
The symptoms of cross-over, syphoning (potential negative health consequences) scald potential (read: injury or death of the young ones) are significant indicators of potential life safety, health and general plumbing code violations.
Now, keep in mind if all the health issues are ruled out (no cross over - no back syphoning, maintaining minimum water pressure, etc.) AND if anti-scalding safety precautions are put into place and/or the overall hot water temperature is reduced (but then again there is the issue of potential legionaire's or similiar being atomized in steam/hot water spray if the temperature is too low), and the management doesn't spend the convienence money - you might end up with cooler hot water, occasionally being interupted with cold water blasts - wouldn't be pleasant, but health and safety wise - safer.