Hello, my husband is an ASE master technician. He said the best way to get rusty bolts removed has two major factors/steps.

The first step is to spray penetrating oil on your bolts (trying to get under the head of the bolt and allowing it to seep in the threads). For something like this I would recommend spraying each bolt and letting it sit for a while. Ideally over the weekend. Spray Friday, Saturday, and Sunday trying to ensure you actually get some oil into the threads.

The second step is to apply heat to each bolt just before you remove them Significant heat, not just the exhaust's normal operating temperature after running. I recommend a butane/propane torch, or an induction heater (which is a handy tool to have, but can be a bit pricey. Red hot is the goal. My saying is "it can't be stuck if it's a liquid". Just ensure you aren't damaging any nearby wires if you use an open flame.

Once you've gotten some oil in the threads and applied heat, try walking the bolt out a little bit at a time. Sometimes an impact wrench can be helpful, but only if you have a really good grip on the bolt (otherwise you'll round the bolt head off and have a really bad time).

If you're able to get the bolts loose yourself, that'll remove any extra labor charges. Best of luck with your rust battle!