You can always open the first rar file in 7zip (or equivalent program) without extracting and take a peek at what lies inside. There should be an MKV, readme, and probably a checksum utility. Merely extracting files from within rars is perfectly safe - as you point out, problems may only arise if you open them afterwards.

A trick I like to use if I’m in doubt is to extract the contents with 7zip, and remove all file extensions afterwards. That way the files can’t accidentally be opened by double clicking on them. Once I’ve checked checksums and scanned for viruses etc. I put the file extensions back.

Yoda-sama’s point about not using a work computer to extract is a good one, just in case the contents are dodgy and flagged up as such automatically to your IT people by a virus checker. You could always copy the rars to a USB stick (32GB should suffice for the MKV) and extract at home.

Bluto