While we are wait for the episode of Fluttershy brother to show up this season. I'm speculating on her parents like the fact she dosn't have any pictures or flash back to show like Pinkie Pie, Twilight ,and Rainbow Dash. Then there are no visitation from them either like Rarity's parents are. So do they don't care for her and treat her for being useless. That why she was so intrigued with Starlight Glimmer cult. That why she never hint about her family?

4697221 Maybe her parents ether died or had gotten divorced and did not spend a lot of time with her cause they were always so busy with work and chores . And maybe around the time her parents divorced or died she was at an age were she could take care of herself and did not need a parent to take care of her.

4697243 which still don't explain why she doesn't why she havn't any pictures of them?

4697259 There's no in-universe explanation for that.

Out of universe, it has to do with Habro/DHX not giving her parents a design yet.

4697270
It fact that they should hinted about her family by now since they told us about her brother coming next half of the season like they did with pinkie pie older sister or already maybe it that changling that we saw in slice of life.