Your opponents can not block either Lightning Runner.
Steps
Attack with both Lightning Runners.
Both Lightning Runners trigger twice.
Resolve the first three triggers, adding ({E} magic symbol) ({E} magic symbol) ({E} magic symbol) ({E} magic symbol) ({E} magic symbol) ({E} magic symbol) and chosing not to pay the trigger.
Resolve the fourth trigger, adding ({E} magic symbol) ({E} magic symbol) and pay ({E} magic symbol) ({E} magic symbol) ({E} magic symbol) ({E} magic symbol) ({E} magic symbol) ({E} magic symbol) ({E} magic symbol) ({E} magic symbol) to untap all creatures you control, and after this phase, there is an additional combat phase.