There are three main approaches here: table saw, router table and by hand.
This is not a particularly difficult job on the table saw, with a well-made crosscut sled and dado stack.
Some additional support to the left of the blade1 would be helpful, but all you really have to do is firmly clamp the workpieces to the rear fence on the sled if you're careful.
You could do this on the TS without either a crosscut sled or dado stack, if you take your time and pay attention, and as long as you can attach a tall fence to your mitre gauge.
Using the router table is arguably not the ideal way to do this, regardless if it's basic or fully featured, because of the amount of support the long shelves require. But it is doable especially if you can arrange additional support to the left and ideally can clamp the workpieces to a tall fence.
Another idea I had would be to clamp up the bottom two shelves and use a straight cut router bit with a guide – but consistency might be a challenge?
Consistency with a router in this sort of situation is merely a matter of careful setup and firmly clamping your stop(s).
But a straight-cutting router bit will naturally leave rounded inside corners on your notches. You will have to either go with these, and round the relevant arris on your frame2, or square those round corners on the shelves by chisel or with a corner chisel.
These are bread and butter for hand tools, saw and chisel. After careful marking out of course, you saw the bulk of the waste away and then (if necessary) pare to your layout lines; if your sawing is very good all you'll be using the chisel for is cleaning up the inside corner.
Traditionally you might be advised to gang the shelves together and do each corner of all of them together in one go, but many people would prefer to do this one at a time. Takes longer but much less chance of a screw-up that affects more than one shelf!
1 Assuming the fence is at the right.
2 Another possibility is to lean into it and round all of them to add an unusual feature to your shelves.