Having replaced many an airbag, here's what I can tell you: It's not hard, but it isn't fun either.
Are you sure that those are the only two things that deployed? Before I had a scan tool, I spent many hours trying to figure out why the airbag light didn't go out when it was a stupid pretensioner that didn't even look blown. I'd recommend buying a scan tool that can talk to the airbag module, which should cost about $100. If you don't think you'll ever need a scan tool again, find someone with a scan tool that can talk to the airbag module and beg for help. It will be worth it to be sure of what you need.
The curtain airbag (when not deployed) looks like a long sausage attached to several mounting brackets that are bolted to the roof structure. There's a harness connector over the rear door that connects to the explosive charge that inflates the airbag. All that is covered up by the headliner, which is then held in place by the A, B, and C pillar plastic trim pieces and the sun visors and grab handles.
The sequence is to disconnect the battery, then remove the trim pieces, visors, and grab handles. Watch videos on youtube on how to get the trim pieces off without breaking them. Then pull the headliner down a few inches, enough to get at the airbag bracket bolts (be careful not to add any more creases to the headliner, they don't ever disappear once created). Unplug the harness connector, which has a little plastic locking clip you don't want to break (more youtube videos). Put in the new airbag, bolt it down, and attach the harness connector. Don't forget to snap down the locking clip. Before you put the headliner and trim back, you're going to want to test it, but since you have multiple bags to replace, do the rest of the repairing before you put the trim back.
For the seat, just go to a junkyard and buy a used seat. Sure you can replace the bag and sew up the seat, but it will take you hours and if you use the wrong thread the seam will either fail prematurely, or fail to rip in an accident and kill you. Just replace the whole seat. Again, disconnect the battery before disconnecting anything. Youtube videos will show you how to replace the seat.
Once everything is connected, reconnect the battery and start the car. The airbag light should go out after 5 seconds, but wait at least 15-20 seconds before celebrating. Sometimes they come back on. If it does, go back to the scan tool to see what the problem is. Once the light is out and stays out, then put all the trim back (been there, did it twice, didn't like it).
Hope this helps.