I'm so sorry you had to find us, I understand what you are going through. My
Mum also had a bypass surgery along with metal stents and it worked for almost 2.5 years.. For about 6 months she had an external drain so I do have some information on how to handle external drains. Coming to your questions:
1. External drains are def more prone to infections which lead to cholangitis (bile duct inflammation due to infection) but then keeping the area dry and clean really helps. My advice for you is to keep checking the dressing to see if it's wet and gooey, if it is then get it changed as often as required by a qualified nurse. I do think it's better to have a nurse who's got some experience with external drains, etc. Also I learnt to change the dressing and sort of clean up the area myself. I don't know about any redness near the area, I don't think it's a cause of concern but do check with the doctor.
2. Chemotherapy at low doses is not recommended since it won't be effective, that's what my doctor told me. Also if he has high jaundice chemotherapy is not suggested at all. He's 88 and I can't say how he would be able to take any side effects of chemotherapy as well.
3. The end stage is very difficult to say, for my mum she had high jaundice, ascites ( fluid collection in her abdomen and legs) and she stRted feeling very tired, didn't eat much, slowly became immobile and then lost her consciousness. Basically these are symptoms of end stage liver disease, I can't say exactly about your dad because it's different for each person.
4. Cherish every second you have with him, talk to him about all the good things, make him laugh and feel better and that you are there for him. The one comfort they will get is seeing loved ones around them happy with their lives, and being by their side.
I wish you and your dad, mum all the best!