Take a file, a fine toothed file, a small one, and scrape a nick through the tough outer seed coat of each seed. Or one could rub the seed on coarse sandpaper. You should see the color change to know you have scraped away enough of the seed coat.
Then soak in water for 24 hours, then stratify for 8 to 12 weeks in the refrigerator. THe cold stratification will give you better, more uniform germination. It might not be absolutely necessary.
The seed coat is very hard. In their native habitat the birds, and insects and ruminants like deer, all chew and or digest away part of the outer seed coat before germination occurs. The redbud in my yard drops thousands of seed every year, but I only get handfuls of seedlings as volunteers. The majority are either eaten or never get their seed coat scarified enough to germinate or I'd have thousands popping up in the year.
Note: Redbud is a legume, if you have soil that culinary legumes have been growing in, beans or peas or other pulses, use some of that soil to inoculate the soil you are germinating the redbud seed in.
I think redbud are a beautiful garden and landscape tree. Well worth propagating. I have seen many a beautiful trained for shape garden tree, essentially Niwaki. They are a problematic species for bonsai. But do try. Do put at least a couple of your seedlings into the landscape as garden trees.
