The spelling of the word "uterine brothers and sisters" is relatively straightforward. "Uterine" refers to siblings who share the same mother but have different fathers. The pronunciation is [yoo-ter-in broh-th ers and sis-ters], with the stress on the first syllable of "uterine." The "u" sounds like the "oo" in "moo," and the "e" at the end of "uterine" is silent. The "th" in "brothers" is pronounced as a voiceless dental fricative, like the "th" in "think."
Children of the same mother but of different fathers.
A practical medical dictionary. By Stedman, Thomas Lathrop. Published 1920.