Softener, humidifier, and AC drains - into trap or arm?

I'm replacing a corroded copper drain line in my crawlspace that services the kitchen sink up above. Currently, the AC, humidifier, and water softener all connect together and drain into a hole somebody drilled into the kitchen sink drain in the crawlspace. The drain hose is just siliconed into the hole and leaks, not to mention the sewer gas that comes back up through the hose.

What I'd like to do is re run separate drain hoses for each, then attach them properly to the drain in the crawlspace with a trap. But I'm not sure of the best way to do that. The only ways I can think of are to 1) simply run the hoses into a trap and secure them and 2) have three separate traps bushed down with hose fittings.

Which if either of the options should I do? Is there another option I'm not thinking of?

NONE of those appliances should be "sealed/secured" into their connection to the drain. In fact, they should all be connected with air gaps, and the crawl space is NOT where the trap should be located.

I didn't think about the chance of a backup. I can add a new trap off of the kitchen sink drain in the closet opposite the sink where there all of the appliances are located to keep the trap out of the crawlspace. I was thinking I could do this and put a floor drain fitting into the standpipe, and secure the hoses into the grate of the drain. This would be the same as installing them into a floor drain which would provide the air gap as long as the hoses are secured properly. Any problem with this configuration?

Mine are run into the washing machine standpipe. The boiler's condensate uses a pump, the humidifer overflow is gravity. Not sure this helps.

Put a 4" x 2" reducing coupling on the end of the riser and secure the drains ABOVE it.

Good. That was essentially my plan but using a floor drain grate to secure the drains to. Thanks.

Depending on HOW you used the floor drain grate, you might NOT have air gaps on the pipes. An "air gap" means the drain lines are fastened so they terminate ABOVE the drain pipe, not hang into it.

I ended up getting an atrium grate. The hoses will be secured well above the pipe.

They need to be above floor level for an airgap. Not just the pipe.