EXCLUSIVE

Two powerful NBA families are set to be linked by marriage -- with Steph Curry's brother, Seth, proposing to Doc Rivers' daughter, Callie ... and she said YES!!

TMZ Sports has learned ... the Blazers guard popped the question to his longtime girlfriend in front of their families at Ruth's Chris Steak House in Charlotte on Thursday ... with brother Steph and father Dell present.

Doc, Austin Rivers and the rest of the Rivers gang was also on hand for the special moment.

It was the perfect op for Seth to get down on one knee ... considering it was Valentine's Day and everyone's in town for NBA All-Star Weekend.

Callie tweeted about the big day, saying "2.14.19 was a DAY. so thankful & blessed & loved & happy & positive & complete."

2.14.19 was a DAY.

so thankful & blessed & loved & happy & positive & complete 💕💕 @CallieRivers25

Holiday basketball games are gonna be AWESOME!!!!!