Catalytic converter notice nuts on one side?

I think the "pins" you're referring to are the bolts but they don't have hex heads. Instead, those are pressed in and have splines under the heads to keep them from spinning. All you do is run the nuts off, then use a small hammer to break the gasket seal free. It's common for the nuts to be rounded off, either due to rust or from use of a 12-point socket. Don't waste your time trying to remove them if that is the case. Use an air-powered cutoff tool, or an acetylene torch to cut the nuts off, then use a hammer and punch to push the remaining parts of the bolts out. Everything can be reassembled with regular hex bolts and nuts. Use the better grade 5 or grade 8, (I can't remember for sure), but you want something stronger than the cheap, unhardened bolts as there will be plenty of pressure on them.

To slide the hanger brackets out of rubber bushings, I use a large flat-blade screwdriver to open up the hole in the bushing, then spray in some Silicone Spray Lube and let it work around. That stuff goes on like water, and when it evaporates, it leaves a film of "slippery" behind. It is excellent stuff for sliding on heater hoses, and for any other rubber parts that fight you. Don't get it anywhere near rubber parts that contact brake fluid. Any petroleum-based products that get into brake fluid will result in a very expensive repair.

It's easier to slide the bar out of the bushing with the bushing still wet with Silicone. Use the screwdriver to help get it started over the hump on the end of the hanger. There's usually rust built up in there too that is going to crumble off. Once the entire bushing is started over that hump, use your pliers or pry tools to work it off the rest of the way. There's usually a second bracket on the frame that goes through the other half of the bushing. Lube that one too so you can work the bushing back on both of them at the same time.

Spray some Silicone on the bushing too when installing the hanger. That will make the parts slip together by hand very easily.