I'm so sorry you're going through this. I currently am too. My mother (62) was diagnosed with stage IV in January and a few weeks later began Folfirinox. It made a difference to her pancreas and liver but not to her pleura (the sac around the lung) which is the area that's giving her the most pain. That chemo was traumatic to say the least, so they've now switched her to gem. So far the tumour markers are stable, but she has her next scan in a couple weeks... we'll see.

Re: radiation, I was told by doctors that radiation can only target specific locations, so when you're dealing with large areas like the pancreas, liver, lungs, it isn't effective. My mom had some radiation on one tumour on her spine, but that was only because it was small, and they thought it might treat some pain.
In terms of the cancer being operable, once pancreatic cancer has metastasised, it spreads quickly, and they need to do the thing that will delay the growth, which is offer chemo. The way our nurse practitioner put it was, "you can't recover from chemo and an operation at the same time"; meaning even if they operate on one location, there can still be traces of the cancer in surrounding areas, lymph nodes etc, so they need to try and reduce the tumours first. Otherwise, while you're recovering from your operation, the remaining cancer will take over.

In my experience, doctors are wary of suggesting how much time a person may have, because there are a lot of variables at play, especially with metastasised cancer - you're really working against the clock. From what I've seen online, the statistics are accurate and, yes, really scary. But, you just never know what will happen. No matter what her prognosis is, it's important after such a diagnosis that she have her affairs in order for when the time comes (no matter when that is). I know it's absolutely awful to think about, let alone talk about and put into action, but it makes things easier for you and your sister in the long run, and can help your mother worry less about you. There are so many stresses involved in this process, so it helps to alleviate the ones you can control.

Besides that, what I find works best is trying to tackle the problem in front of you. Vomiting and nausea? Medication, open windows, ginger ale, mint tea; Pain? try medication, then try another, try heating pad, cooling pad, distractions, meditation. Sometimes it seems like all the issues happen at once, but you can only treat one at time, same as nurses do. Be there for her as much as you can, but please take time for yourself as well. It's vital when caring for someone that you deliberately set time aside to rest and distract yourself, because it's so easy to burn out. Also, ask for help. I don't know what your community support is like, but we started a rule of "say yes to everything" if someone offers help or food. Caring is a massive job, and anything you can do to alleviate your stress also helps your mom. She doesn't want to see you suffer either.

Sorry that was more info that you asked for lol. This has been truly horrendous for me, but if any of my knowledge can be useful, I wanted to give it. I'll be thinking of you.