If I summon Breakneck Mech readied because I have 2 mech tokens at a battlefield, can I move the Breakneck Mech and one or two mech tokens over at the same time to attack the enemy unit at their held battlefield?

Yes, you can move the Breakneck Mech and your Mech tokens to the same battlefield simultaneously to attack, provided you follow the rules for a Standard Move.

Ruling

According to Rule 144.3, you may perform a Standard Move for multiple units simultaneously. When you do so:

• Destination: All units involved in the move must have the same destination (Rule 144.3.a).
• Origins: The units do not need to start from the same location (Rule 144.3.b).
• Costs: You must pay the cost of exhausting each unit involved in the move simultaneously (Rule 144.3.c).

Because Breakneck Mech grants Ganking to your other Mechs, your Mech tokens gain the ability to move from battlefield to battlefield (Rule 144.4.c.1). As long as the battlefield you are moving to is a legal destination (i.e., it is not currently involved in a combat with two other players, per Rule 444.2), you can declare a single Standard Move action to move the Breakneck Mech and your Mech tokens to that battlefield at the same time.

Important Considerations

1. Exhaustion: You must exhaust every unit you are moving as part of the cost. Since the Breakneck Mech enters play ready (if you control another Mech), it is eligible to be exhausted for this move.
2. Timing: You must perform this during your Main Phase while the game state is OPEN (no chain exists). You cannot perform this move during a Showdown or if a chain is active (Rule 144.1.b/c).
3. Combat: Moving units into an occupied enemy battlefield will cause a Showdown to begin (Rule 447.1).

This is my interpretation based on the Standard Move rules and the Ganking keyword. No official FAQ exists for this specific combination of units.