Good advice given already.
Unless all 3 of you have a lot of experience calling coyotes together, I would strongly suggest starting out your first few stands sitting next to eachother. After you do a few stands, then you could then decide to occasionally spread out a little. Unless your grandson is an experienced hunter, either you or your son should be sitting next to him the entire trip.
The decisions you make before you start calling are often the most important. I'm always trying to improve my stand selection skills. The more I learn, the more I realize some of what I thought were very good stand locations are not the same stand locations I would select today. Every stand is unique and I have to make compromises of some kind on every stand.
These are some things I prioritize when selecting a stand location
#1 Elevation so I can see/shoot approaching coyotes more easily
#2 Wind in my face with a low probability of coyotes coming from downwind side
#3 Easy way to approach stand location with minimal risk of coyotes smelling, seeing or hearing me
#4 Sun at my back
#5 Shady spot for me to sit
#6 Large bush or tree behind me to block my outline with minimal bushes or trees directly in front of me to impede my ability to shoot or see coyotes I call in.
#7 Calling a place I know has a lot of coyotes that haven't been educated by other callers. A place that has a bunch of coyotes and no one else ever attempting to call is like a unicorn and probably doesn't exist. However, some places have much higher densities of coyotes and some places have much more calling pressure than others.
The experience of the people I'm with, the terrain and wind will all be factors when deciding where I think each hunter should sit. Inexperienced coyote callers will either be sitting right next to me or next to someone with experience. I've tried placing experienced big game hunters that were inexperienced at calling coyotes 50 or 100 yards from me and it almost always causes problems that are not worth the benefit of having additional shooting lanes covered. After someone gets a little experience, I'll have them decide where they want to sit and then I may adjust the exact spot I sit to cover the downwind better. Sometimes guys with less experience than me come up with better ideas than I have and I'm always trying to learn something new.
Sitting all close together has the advantage of being able to communicate more easily. When calling with other people it can also be more fun to sit all together.
Sitting spread out has the advantage of having more shooting lanes and can be more effective for killing coyotes that would otherwise get away.
I was calling with my dad last week. On 2 of the stands we sat next to each other. On one stand we were 50 yards apart. One stand we were about 100 yards apart. The only coyote that we saw was on the stand we were sitting 100 yards apart. A wise old male that was missing a couple teeth. My dad wasn't ever able to see him. I was able to drop him at 364 yards when his body language started to act too suspicious. We may have killed that coyote if I had decided to sit next to my dad but I believe us spreading out on that stand gave us an extra advantage.
I hope you have a safe and enjoyable trip. It may just be bad luck for me, but I've made about 10 stands in NM in the last couple months and haven't called in a single NM coyote this fall. Even if you don't call in many coyotes, you should have a great time on an adventure with your son and grandson.