Two card counters at the same table, raising and lower bets in unison is very bad. It is extremely easy to spot. Even if they are playing different counts and different bet spreads, the raising and lowering together is a major red flag.

For this reason it was always an unwritten rule that the second counter to the table would immediately exit once they realized the situation (you don't always know when you sit down, until the count goes positive, and both start raising wagers). Of late sometimes the second counter no longer observes that unwritten rule or courtesy, putting both in danger.

I know solo type card counters that were "linked" to other counters and teams in databases, simply because they were at the same table.

If you are a solo type card counter in it for longevity, it just isn't worth it.