The 1892 RLDS edition accidentally replaced this with his in this passage. The use of his would work theoretically, but the sources otherwise read this here. Also note the seven occurrences of “this people” elsewhere in this first part of chapter 29: verses 7, 10, 11 (three times), and 13 (two times). Here in verse 9, the 1908 RLDS edition restored the original this to the RLDS text, probably by reference to 𝓟.
Summary: Maintain in Mosiah 29:9 the earliest reading with its use of this rather than his (“and also this people”).