In Unicorn each process establishes its own connection pool, so you if your db pool setting is 5 and you have 5 Unicorn workers then you can have up to 25 connections. However, since each unicorn worker can handle only one connection at a time, then unless your app uses threading internally each worker will only actually use one db connection.
In Sidekiq, the connections in the pool are shared across threads, so you need to have at least one connection available per worker. If you have a concurrency of 5, then your pool needs to be at least 5.
Having a pool size greater than 1 means each Unicorn worker has access to connections it can't use, but it won't actually open the connections, so that doesn't matter.
The total number of actual connections your app requires, unless you're using threads in your application code (and they don't share a db connection), is one per Sidekiq worker plus one per Unicorn worker.