Should Congress people who supported Trump's attempt to overturn electoral college results prior to yesterday be charged with sedition?

No. They only asked for an investigation.

In fairness, several states had sent letters to Congress saying that they would like to re-think their certifications but Congress chose to ignore them.

Why would it matter if Congress approved the wrong Electors?

The last four plus years of Democrats = sedition ~ conduct or speech inciting people to rebel against the authority of a state or monarch.