They can focus on particular skill to learn and offer such on online working platforms like fiverr and upwork. An example of such a little bit simpler skills could be transcription. If they're good at it, it will spin good money for them too.They can venture into affiliate marketing, this type of work is not time consuming. Also I will suggest they learn skills that are in high demand online, which they can offer to clients as a freelancer. These skills might include domaining, web design, programming, transcript work, writing, etc.