arteries can transport much more oxygenated blood than is necessary for the tissues that are fed from them, so they have actually quite some reserve capacity.. Therefore slight blockages do not give problems. Normally it are the 80+ % blockages that give the problems.
They can be bypassed with bypass surgery or they can be opened with stents in a minimally invasive angioplasty procedure.
Your father has one in the RCA after the crux. I think that surely needs treatment and at the moment will be the main cause of symptoms.
The other blockages are 70% or less and could perhaps be managed with medicines alone.
There are two scenario's:
-If your father would get surgery, they will probably, besides the problem in the RCA, also treat the other blockages in the LAD and RCX.
-If they would try to place a stent at the crux position and leave the other blockages as they are, that perhaps could be a good solution for the time being. The coming months would then show if that solution is good enough and durable.
If I was in your fathers position, I would certainly discuss the second scenario with the cardiologist as this means very short recovery compared to bypass surgery. The first scenario would still be possible afterwards if necessary.
hope this helps you a little. Please feel free to get back if you still have questions.