Father in law in palliative care – how to handle with the kids?

So my kids are 9 and 6.  My wife’s dad was admitted to the hospital with severe abdominal pains 4 weeks ago, and has been diagnosed with liver cancer (and likely other cancer(s) that are still being investigated).  Also having lung and heart issues that between that and strong pain killers, is greatly affecting his energy and cognitive abilities.  Got news today that it’s stage 4, so prognosis is obviously very negative.  With the heart/lung complications, he could pass fairly suddenly at any time, or it could go on for months. 

He's always been a great influence in our lives, especially our kids.  I’ve always said I won the in-law lottery, and they’re both very engaged with our kids, so it’s been especially tough.  Our kids know he’s in the hospital, and sick, but we haven’t told them how serious it is.  They’ve kind of left it up to us if we want the kids to visit (they haven’t yet – he’s an 8 hour drive away at the moment), though we think he’d kind of lean to the “not” side (he hasn’t wanted anyone other than his kids and siblings to visit so far). 

We’ll have to tell the kids soon, and decide if we want to bring them to visit.  I’m torn – it could be good for them to say goodbye (or at least see him one last time), but also currently their memories of him are him as a healthy, happy person.  Visits could go either way.  He could be alert and in good spirits, or tired, in pain and confused.

We’ve had our 2 dogs pass away in the last 18 months, so death isn’t a completely foreign concept to them, but this obviously much different.

Anyone gone through the same?  Any insight or suggestions?

Thanks