Normally notification of the IRS is done through the bankruptcy filing. I had someone who owed federal tax debts and we sent notification to a location in Philly and to our local US Attorney. So you shouldn’t have to do that.
I don’t know about any requirements in Chapter 7 for filing any back tax returns but it is always better to file the tax returns before filing bankruptcy. Any potential refunds become part of the estate so you’d need to know what they are so the bankruptcy attorney can exempt them (if possible). If there are taxes due then better to get it on the books so it can be resolved in bankruptcy or through other tax resolution options.
Finally, generally any other parties who are jointly or severally liable do not benefit from the bankruptcy discharge. The IRS can still collect from them. Now in Chapter 13 there is a so called “co-debtor” stay which means the IRS cannot collect against any parties who are jointly liable until the Chapter 13 case is closed or dismissed. In this possible Chapter 7 case, the IRS can collect against the other parties for the full amount due.
Those are my off-the-cuff thoughts. Good luck.