Did you check the relays while you checked the fuses? It could also be a bad switch but also check the wiring.

I would suspect a corroded or worn out horn switch on the steering wheel.

Your testing as a DIY mechanic will be limited on that 2014.

Back around 2007 those minivans had a replaceable horn relay. You could pull out the horn relay, jump relay sockets 30 & 87 and if the horns beeped, you'd swap out the relay and if that worked your problem was solved.

But by 2014 the horn relay was soldered onto the TIPM's (Totally Integrated Power Module's) PCB (Printed Circuit Board) which is the underhood fuse box (the bottom side of it which you can't see unless you pull it out).

Let's look at the horn circuit and see what you can test as a DIY'er. (use your fingers to "unpinch" the image larger or ctrl +)

So as a reference, those 2 fuses, M22 and M23 are the horn fuses you've already checked in the underhood fuse box (TIPM)

The way it works is when your dad pushes the horn on the steering wheel a "Horn ON" request signal is sent through the data network and is received by the TIPM which it sends it to the Horn Relay Control which provides a Ground to the Horn Relay's control coil (energizing it and closing the load side contact) to send battery power through fuses M22 & M23 to toot the horns.

Here's the drill:

1) Grab a test light.

Hook the alligator clip to the negative battery terminal.

Touch the test light's probe to one of the M22 or M23 fuse test tabs as someone is pressing the horn on the steering wheel.

If the test light lights up, you know that the TIPM is receiving the "Horn On" request when the horn is pressed on the steering wheel and that the relay is working.

2) Go down to the horns and remove the connector.

Test for Power on 1 terminal when the horn on the steering wheel is pressed and check for Ground on the other terminal.

If you have Power AND Ground there then you need to replace the horns.

If you aren't getting Power to the M22 & M23 fuses when the horn pad on the steering wheel is being pressed then you need to find somebody with a scanner that can see if the "Horn Request ON" signal is being received by the TIPM.

If the "Horn Request ON" signal is being received by the TIPM but it isn't energizing the Horn Relay, the problem is likely a faulty horn relay on the TIPM's circuit board.

If the "Horn Request ON" signal isn't being received by the TIPM, then you'd turn your attention to a problem with the steering wheel horn control