The room for their opinion is in peer reviewed medical journals. Short of conducting their own study, they could, for example, write a dissenting letter to the editor, or submit what's known as a "brief report." Posting to Youtube for clicks and views is to not take seriously their own knowledge. Covid-19 is a very serious issue; on the chance that your two senior scientists have information that the world needs, the appropriate venue is in the medium scientists and doctors use to communicate with each other.

Also, what does it mean to be "skeptical" of "the" vaccine? There are several vaccines. Were they skeptical of mRNA? Viral vector vaccines? All of them? Do they think that the covid-19 vaccines secretly don't work?