I had quad bypass 10 years ago this May. I went in for an angiogram, and they would not let me leave the hospital. I was a couple decades younger than your Dad is.
Here's how it goes. Have a pillow for him to clutch when he cough or sneezes. That will help but it will still hurt like hell for a while (3-4 weeks?).
Unless his doctors say otherwise, they will want him up as much as possible, even if just standing up for a moment, before sitting back down. And he will need to walk - a lot. Within a few weeks it will be very easy for him - I was up to a couple miles within 2 months.
There will be cardiac rehab with stationary bikes, and hand weights to bring full motion back to the arms, back and chest. Remember, your Dad got cracked open like a lobster claw, and they have wired his sternum together.
They took arteries out of my arm since the veins in my leg were too small, and the second worst part was when they removed the arm staples. First was the damn coughing - it feels like the whole rib cage is flapping open at first. The chest incision was closed with steri-strips, so removing those was a piece o'cake.
Surgery in May, clean bill from the doctor to go horseback riding on a wild remote ranch in Wyoming in August.
The meds they will put him on will help considerably with the whole family genetics/chemistry thing, which was part (only part) of my problem. My BP is 130/70, cholesterol in the 115-120 range, HDL/LDL in perfect ranges, etc.
Sorry that this happened, but it is one of the things they do well in medicine these days. Tell your Dad "Welcome to the Zipper Club" for me!

It should give him a whole new lease on life.