Water rooting works almost every time IF you change the water every few days. A 12" cutting, with all the bottom leaves removed, is ideal - don't let the bottom of the cuttings touch the container, though.

Yes, you can get 2 nice cuttings from the branch you have. When you see roots about 3" long, plant them in soil and keep in the shade.

Water when the soil is dry 1" from the top of the pot. They don't like being transplanted, so choose a big pot from the start.

I didn't know they don't like being transplanted. Do I have to put them in a pot if they're going to eventually go into the ground, or can I transplant them into the ground?

You can skip the pot and go right to the ground. Oleander once established is almost impossible to kill. Al

I sure hope so. I've killed them in the past, though.
Well, I had help from Oleander moths. Lots of them.

you probably know, but avoid the sap - highly toxic

I have gathered 6 cuttings (3 red and 3 white) from large Oleander plants I found in a closed-out Church garden. All the cuttings were between 8 to 10 inches. I chose the ones had no blemish and side shoots. I used a 2 litter Sprite plastic bottle and cut the top 4 inch off. I filled it with plain water and used 2 drops of miracle-gro houseplant food. After 3 weeks - roots formed in all the cuttings and I saw new growth began.