Dome lights will not turn off, fuse sparked when I removed one

The fuse would arc because of the lights being on and drawing power. The issue could be a bad switch that controls the dome lamps, a possible test would be to use the dome light bypass switch. If the bypass turns off the interior lights, then the issue is likely a switch as the bypass opens the circuit. Failed door switches are common as is the circuit wires grounding out as that is what the switches do. If the bypass works, the next step would be to remove the switches one at a time and disconnect them. The one that turns the lights off is the one that's stuck on.

If the dome override doesn't turn them off then it isn't a switch, Which lights are on? All of the dome lights or just one or two lights? The way they work the orange wire carries power to the interior lights from that fuse, then the lights are grounded on the other side to turn them on. Do you have remote keyless entry? That has a timer that turns the interior lights on when activated and it's possible it has a problem. Or it could be the dome light control module. However, if it's not all of the lights turning on it's possible it's a short only for that light.
With the fuse out the lights should go out; they only get power from that fuse. There isn't any draw with it out.

Okay, that changes things a bit. If it's only those lights that are stuck on it's likely a localized problem with the white wire that grounds to turn them on/off. Is this van equipped with the courtesy lights in each door? Does it have a roof console? How about the map lights in the center lamp location? These vans were built using multiple layouts, but many still have the wiring for the other versions tucked away. Those two lights are fed power through the orange wires and are turned on and off with the white wire. Except for the center lamp which has map lights, it has a switch that turns the map lights on and off that could ground the other lights if there was a problem inside the lights.

Yeah, the reading lights are map lights. They got that name way back when paper maps were common, and the navigator read the map but wanted to keep the light away from the driver.
Do the map lights turn on and off like they should? So far it sounds like an issue with the white wire that grounds the lights. One item that might help would be to unplug the interior light control module, it is mounted up next to the OBD port under the dash. It controls most of the interior lights and unplugging it might isolate the fault. If unplugging it turns the lights off then it is faulty, if it makes no change the issue is the white wire, probably a grounded splice point behind the headliner.

Where you outlined could be the area, but all of the lights ground through the same splice so if both of those lights are on, the others should be as well. That is why it's difficult, they have multiple lights connected to the same points.

Okay, try again on that module, it's possible that it got hot and melted together. That could be what is holding it in and possibly the failure item as well. Attached is a cleaned-up version that removed the options yours doesn't seem to have. The lights you have stuck on are all connected through both the orange power feed and the white control wire. I would start with the simpler stuff first rather than going after the splice. Unplug that module, if the lights are still on then, disconnect the dome light switch in the dash. I'm thinking it is one of those that failed and is sticking the lights on.