ANSWER:

You are not the religious police!

Advise those close to you privately and with knowledge and wisdom. Once you done that, you move to someone further in the circle and so on. 

I went to a picnic at a park in town with Muslim community of my town & I noticed that almost all the men were completely shaven and around half of the women were without hijab. When I asked they said they believe that beard is only mustahab & sunnah but not mandatory and they also said they believe it is only mustahab for women to wear hijab & only a personal preference. How could I advise them?