nasty

My wifes Grandmother has some issues in her only bathroom in a 1960's home. Sometimes the toilet water will come up into the bathroom and kitchen sinks(the kitchen sink is on the other side of the wall from the toilet.). What could cause this? The plumbing and fixtures are all original.

The drain is clogged. Get it professionally augered.

toilet

The toilet water cannot come up in the sink unless the toilet is on the upper floor and the sinks are on the first floor, or at least on a lower floor than the toilet.