The lawsuit from the parents of the victims are suing Remington for "knowingly marketed and promoted the Bushmaster XM15-E2S rifle for use in assaults against human beings.", not just for the death of their family members. The comparison you posed is a bit inaccurate.
This, in my opinion, is completely in line with what we do consistently. We hold the alcohol industry accountable for marketing to youth knowingly. We hold tobacco companies accountable for the same thing. Most recently, the Trump administration has been working on an e-cigarette ban and Juul has ran into alot of trouble for marketing to kids. This lawsuit is much in the same vain as the aforementioned. These guns companies have very questionable marketing tactics and lobbying and this lawsuit is just a way to address that.
I for one, while not anti-gun, would not mind seeing these companies along with all other corps involved in the military-industrial complex dismantled.