Can you cast one cantrip, modifying it with "Twinned Spell" (Fire Bolt) to target 2 creatures, and then cast another cantrip as a Bonus Action (Fire Bolt), using "Quickened Spell" to target one of the previous creatures or another creature?
By the Rules as Written: Yes, you can.
First: You can cast two spells, one being a cantrip (PHB, p. 202). Since both are cantrips, your example works.
You can't cast another spell during the same turn, except for a cantrip with a casting time of 1 action.
Secondly: You can only add one Metamagic option to a spell (PHB, p. 102). Since the wording indicates it's only limited to one per spell and not per turn, you can add as many Metamagic options as you wish on different spells, as long as you follow the previous rule.
You can use only one Metamagic option on a spell when you cast it, unless otherwise noted.
Therefore, you can cast two fire bolts, each one with a different Metamagic option.