Can "life" be used in reference to more than one person?

This is perfectly correct (ngram).

Examples

• (ref., 2008) It reflects the priority of work in the life of many British contemporaries and, albeit indirectly, it invokes death through the implicit idea of stress resulting from a 'work-life' imbalance.

• (ref., 1992) The life of many Christians today is largely a pretense.

• (ref., 1975) In the monastic life, it is extremely important that we take account of this concept because, in fact, we have to face with sorrow the bitter truth that the life of many monks and many dedicated women, and many other dedicated people, […]

• (ref., 2010) It was a model that ignored the realities of the life of many families, and was a model inaccessible to millions of poor families (Heiner, 2002).

However, "the lives of many" is not wrong and it is much more common (ref.).