Adding more than an inch or so of soil around the root system will likely have a negative impact on the trees. It's the same as planting the tree too deeply. They look fairly mature. Were they there when you moved in and how have you been watering them prior to the demo?

Digging the holes you are describing will cut through roots, larger roots and feeder roots unless your digger is incredibly careful and lucky. The majority of the roots are likely in the top 18" of soil and may spread out 20 feet from the trunks. Would you be digging 1 hole per tree and how far apart? They might compensate, regrowing roots, but if you're trenching through the canopy I think you're going to have problems.

Having said that, I think utilities come first. If the electrical and irrigation installers say this is the best route, that may be what you have to do. Just know that you may damage the trees.

Gonna break this in parts since I keep loosing everything.

1) They’ve been here for as long as my neighbors can remember. They looked to be previously watered by a break in the irrigation. I’ve been watering when I remember but I need to run some actual irrigation to them so they don’t need to rely on my memory.

I think I can stick to the back fence and north of the trees for irrigation but husband is going to be grouchy since it’s a lot of extra trenching to get to the garden. Sounds like it’s worth it. I think I can rearrange some electrical needs easy enough plus low voltage...

Speaking from experience you don't want your irrigation to go too close to the tree roots (no where under the canopy). It causes problems down the road with breakage of the irrigation from the roots and then further problems when you have to dig up and cap the broken part (cutting more roots) and reroute the irrigation to avoid it happening in the future. Dig the longer trenches now (once) because if you don't you may find yourself doing it twice.

rossnagl asked " Can I add dirt on top of the roots? "

If i was going to add anything over the top of the roots it would be compost and or mulch.

Why is it that you want to add something?

There is a very old plastic waterfall that has to get pulled out. The plastic is in pieces and it’s not going to be safe for kiddo. The hill has eroded quite a bit, it’s sloughed into the yard, and it now drains towards the house. And then it’ll be far enough to the right to not impact the trees but I’d like to add a bit of edging and soil. Just enough to give myself a better way to access the plants, weeds, and irrigation