Third person plural indicative and dative present participle

[Dave Langlois]

Apologies beforehand if this is a greenhorn question but I only started learning ancient Greek a month ago to divert my dotagem and one thing has got me particularly confused: for a regular omega verb like luw, the third person plural indicative luousi seems to be the same as the third person plural dative present participle.  So my question is: “how can you tell them apart in any sentence, which in both cases will presumably contain an implicit or explicit third-person plural subject? Many thanks beforehand.