I'd use a slightly diluted mixture of TSP or Spic n Span and water and wash down all walls/ceiling. Upholstery and curtains will have to be cleaned and deordorized. Any carpet will have to be cleaned.

Good luck. A full house cleaning will be quite a chore.

Patser is right about washing down all the walls and the ceilings, but you don't have to do it all right now. Focus on areas where he spends the most time and work out from there.

Fabuloso makes a lavender cleaner that leaves a very light scent. I've used Fabuloso in my carpet cleaning machine instead of the manufacturer's shampoo (probably this kills the warranty, but I like the smell better). White vinegar works on smells that don't come out with cleaning. You can use Febreeze, but it will be more expensive. I quit smoking 24 years ago, and I saved money that would have gone up in smoke and bought myself some really expensive, real perfume.

Note: Depression (weeping over old movies and things, for example) is normal after bypass surgery. It will pass, but it scares a lot of men. It helps to have a buddy who has been through it.

I work at a restaurant that still has a smoking section, so I know how to get smoke out of fabrics! For curtains, bed linens, and other fabrics that can go in the washing machine, use a little extra detergent and a cup of baking soda. Hand wash the other fabrics using the same things. Cleaning the carpets with the Fabuloso(as suggested by chambleemama) is the best way to quickly start freshening up his home.
If the paint in the home is glossy, using a mixture of two parts water/one part vinegar will clean walls wonderfully! The brightness will surely cheer him up!
Use wood oil soap on the cabinets. It gets out grease and smoke and still livens up the wood.
Good luck and it's great you're helping your sis. That's a huge job!

It is tough to get smoke smell out of wood furniture. I tried Murphys Oil Soap and Orange Glo cleaner. It helped about 75% of the odor. Also sprinkle baking soda in all the drawers and vacuum it up a few days later.

Good luck.