You would have to contact Medi-cal to see if it would affect their eligibility. If they received insurance through the Marketplace, if you claimed them, then it would affect their Premium Tax Credit.
The benefits of claiming them is your income would be decreased by $6,450 and you would get an Other Dependent Credit of $500 for each of them. So, you would have $7,450 less in taxable income. If you are in the 24% tax bracket, that would be $1,788 in tax savings. When determining whether or not to claim them, you can keep that number in mind.