What you're looking for is an information interruption to the cluster, which can be from a few different sources. The cluster receives its info from a bus communication network that shares between systems on the van, but the reason why you lose cluster output is still uncertain when you see prompts like ABS or airbag displayed at the same time.
When the bus crashes completely, ALL info is interrupted, which includes systems such as ABS and airbag. If it was only an engine management issue, we could assume with some assurance that the problem originated with the engine controller (PCM for short), but things get muddy at this point.
While it would be handy for us to know that communication with ABS and airbag was still possible during these events, crashing of the communication bus can be from a single cause that involves the PCM, ABS or even airbag. You've somewhat eliminated the cluster at this point...
If possible, I'd recommend disconnecting the PCM during the times when you have all warning lamps illuminated at the same time AND loss of gauge function. If your ABS and airbag come back online at that time, it appears likely that the PCM is responsible for dragging the communication bus down. Unplugging ABS can have similar effects when ABS is the one involved in the problem.
You'll find the PCM located on your van under the hood almost directly above the fan area and mounted to the bulkhead area. It's the 3-connector unit that is roughly 6" x 9" wide. Disconnect all three connectors while you do this test. If you have improved function to the cluster with the airbag lamp going out, you've shown that there is a problem in the PCM's ability to communicate. ABS will remain on during these tests because it gets cheesed when it can't see PCM directly.
ABS is located almost directly below the battery
tray, which can have an effect on its overall health. Heavy battery acid loss over time can corrode the harness and ABS connector, which may account for the problems you see. I recall there being a recall for problems of this sort but would have to check at work tomorrow for specifics on the issue. If you'd be so kind, send me the last 9 digits of your VIN and I could check for recall applicability based on build information.
Give it a try and let me know what you find. A digital voltmeter would come in handy at some point if you continue having problems.