celebrating TET with a local family (Ho Chi Minh City)

Hi! This might sound stupid, but I'll give it a try anyways -)

We've been invited by a local family to celebrate Tet with them, in their grandma's house in the country.
Just to be on a safe side, are there any traditional elements that it would be nice to know in advance and follow?

Like what a guest should bring or is expected to bring? Those yellow flowers? Some small sums of money in envelopes for kids (so I heard - and if so, how much should that be?) Candies?

Anything a foreigner should know about this celebration in a family, given their inner hierarchy (is that serious? So I heard) or who knows what (I am sorry to admit I have the tiniest idea about local traditions and ways, I just know there are some).

Thank you so much for any tips! And happy Tet everyone -)