Unless it is unavoidable, two people 'suspected' of being infected should not quarantine together if they will have contact with each other or the potential to spread the disease between one another. That's because one of them may have contracted the virus and the other may not have, and placing them in close proximity could result in both getting infected. If two people in the same household need to quarantine, then they should do so by themselves, taking the same precautions as if they were trying to quarantine in a space with a healthy person who has no reason to believe they've been exposed to COVID-19.

https://www.ottawapublichealth.ca/en/public-health-topics/self-isolation-instructions-for-novel-coronavirus-covid-19.aspx

Updated 3 December 2020