You can order their death certificates online through the Department of Health. It usually lists where the deceased is buried.

Texas Death Index, 1903-2000
about MRS. Eliza Ross
Name: MRS. Eliza Ross
Death Date: 23 Nov 1916
Death County: Galveston
Certificate: 25362
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Texas Death Index, 1903-2000
about Susan Ross
Name: Susan Ross
Death Date: 15 Nov 1940
Death County: Galveston
Certificate: 50289
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http://www.dshs.state.tx.us/vs/reqproc/who_can_order.shtm