The Rolleiflex Standard has the famous Carl Zeiss Tessar lens (uncoated), Compur shutter, lever wind and focusing knob. No flash sync unless modified. Same lever for cocking and releasing the shutter.
I haven't used a Flexaret, but they have a lever for focusing under the taking lens, Meopta Belar (four elements) or Mirar (three elements) taking lenses, and most have Prontor shutters with flash sync. Most have knob winding, but some models have lever wind. How the shutter is cocked and released differs between the models.
The Rolleiflex Standard is "more class", better shutter and the Tessar is superb, but a Flexaret with Belar and flash sync could be better for colour (coated lens) and easier to use if you use flash a lot.
I have three Rolleiflex Standard, but haven't used them for some time because the low gearing for the focusing knob makes it difficult to focus (for me). The later Rolleiflex Automat feels "snappier" to focus, so I use this camera instead. Same fine Tessar lens. Since someone in your family has a Rolleifex Standard, test how you feel the focusing works for you.
Some people like and some don't like the lever focusing the Flexaret has either, so it's up to personal preference.
