In the US, parents are not considered dependents. They are independent adults. By USCIS rules (see their website), L-1 dependents are spouse and unmarried children under age 21. If they are unable to exist without you, you should decline the assignment.
You may receive insurance from your employer, but they are unlikely to. How do you intend to pay for their medical care even if they just visit you? Just because you want something does not mean it is possible by US law - or is practical in everyday life.
Do you think that elderly dependent will be happy even visiting in the US if they are totally dependent on you? How can you both do your job adequately and care for two dependent individuals? Assistance for the elderly is extremely expensive.
