If two people are suspected to be infected, can they self isolate in close proximity to each other?

Many, many factors: If 2 people surely have the same infection at the same time (not merely suspected of having it) they usually can be put in the same location for isolation. If only suspected of having it, but not confirmed to have it, the risk would be one of them has it but the other does not. If put together, the uninfected person will catch it from the infected person. Decisions are based on risks and benefits!