Neighbours drain

I live in a semi, with the drains flowing from the other half of the semi towards my property and then along to the other houses.
For the second time in less than a year my neighbours drains have blocked - apparently the inspection chamber is half full with sewage.
At the weekend I checked my inspection chamber which was fine, and flushed both toilets in the house - again everything flowed fine through the inspection chamber.
Can I assume that the blockage is in their pipes? My neighbours are elderly, is there anything I could do to help out - if I call in a professional to unblock their sewer how much is it likely to cost? One of our other neighbours has a set of rods - is it reasonably easy to attempt to unblock the pipes myself, or am I likely to do more damage than good? The properties were built around 1950.

Thanks in advance.

Give it a whirl with your other neighbours rods.

Remeber to keep twisting them clockwise so theat they don't undo in the drain; and watch for the pull that can happen when the block shifts.

I was nearly caught out once