E.P.
We went through this process a few years ago when we had to prepare my mother-in-laws home to put it up on the market to sell it. We had to paint all the walls because of the heaving smoking that three people did in the home. Unfortunately, if they are planning to continue to live there, you will have to consider scrubbing the walls, prior to painting, as the nicotine will bleed through the paint. Any hard surface that could be scrubbed, we used TSP (trisodium phosphate). However, because there was so much nicotine on all surfaces, everything had to be painted over, including the cabinets. We also used TSP on wood moulding that had some mildew-stains and it came off. Don't get me wrong - this will require a lot of elbow grease, too. I don't really know if this will ruin your wallpaper and do make sure that your room is properly ventilated.
I used Spic-n-span on their old paneling and so much of the dirt came off, but I had to wash those walls down a few times before the water ran clear. I'm sure spic-n-span is probably safe for those surfaces but lately, it's a little hard to find that product. They now sell it in a liquid concentrate but if you can still find the powder form, it's just as good. I just washed my walls with it before the holidays (just dirty walls - no tar to remove) and they really are streak-free.
This will be a process for you. By the time we put the home on the market, including removing old carpet in some rooms and professionally having the carpet washed in others, it really smelled fresh. It's so good that they are going through this process.
Hope this has helped. Good luck.