His sacrifices shall be wholly burned twice every day continually: The reference here is probably to the burnt offerings described in Num 28.3-8. The burnt offering was not simply a “grain offering” as Good News Translation has it. The pronoun His refers to Aaron and by extension to his descendants. In the first model below the pronoun “Their” refers to the priestly descendants of Aaron mentioned in the previous verse:

• Their never-ending duty is to offer sacrifices twice a day, sacrifices to be completely burned.

• Twice each day, for all time, these priests must offer sacrifices that are burned completely [or, that they must burn completely].

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on Sirach. (UBS Helps for Translators). New York: UBS, 2008. For this and other handbooks for translators see here.