[Don]

I don't have a Tactical, but it should be as straight forward as described above. One the takedown lever is rotated up, there is nothing in the path of the guide rod and spring to stop them. The striker is all that can keep the slide from coming off.
Does the slide seem to operate normal without trying to take it off?
Does it go forward all the way until the barrel is seated?
If it is all the way in battery does the guide rod end stick out any more than usual?
If you put the "open" end of the spring on the rod first that end can slip by the head and jam. If that is the case I will post a description from another similar sounding thread:

Yep, I can jam my pistol!

The guide rods stick out as you say and the slide will not come off. But I got it off without much pain. The trick is to get the takedown lever removed while the slide is in place.

Everything is unloaded right? you will be pointing the pistol in all kinds of directions while you do this stuff.

Lock the slide back. There is a spring end (wire) that rides in a slot in the takedown lever. Actually two slots that are at 90° to each other. So if you position the takedown lever at about the 10:30 position, you can get the wire to set halfway between the slots (on the big diameter of the takedown lever) and poke the lever out from the opposite side. Press on the lever while working the lever around the 10:30 postion and you will feel it give a bit when it hits the right place. Press it harder and it should come out. It did not come all the way out on mine, but it came out far enough to get out of the way of the spring.

Now release the slide and let it forward, and then pull the trigger to release the striker. Now move the slide forward as much as it will go. My guide rod stayed back enough that I could get the front of the spring out of the hood on the slide. If you are looking at the closed coils on the spring this verifies that the open end of the spring is back in locking block. Wiggle the rod and spring around as you push the slide forward and it should come off with just minor force. The force is just the spring stretching and didn't casue any permanent spring damage.

The takedown lever now can be put back proper (it just sticks in and the spring end will snap into place on its own). Assemble as normal and show your brother the right way. It was hard for me to assemble mine wrong, he had to be real determined.