To make one point clear:
WT doesn't say, MS & Elders are appointed direct by holy spirit. There chain of reasoning:
---> Bible was written under the guidance of the holy spirit.
---> So the scriptural requirements for men (recommended for congregational responsibility) were written under the guidance of holy spirit.
---> For this, they (men) MUST meet the biblical requirements for appointment.
---> THEN it can be said of them, that they have been appointed by holy spirit.
*** w13 11/15 p. 22 par. 6 Obey Jehovah’s Shepherds ***
6 When addressing the overseers of the first-century congregation in Ephesus, the apostle Paul pointed out that holy spirit had appointed them overseers “to shepherd the congregation of God.” (Acts 20:28) The same is true of Christian overseers today, since they too are appointed on the basis of Scriptural requirements inspired by the holy spirit.
*** bt chap. 5 pp. 42-43 par. 20 “We Must Obey God as Ruler” ***
Jehovah’s people today follow the apostolic pattern. Men recommended for congregational responsibility must manifest godly wisdom and give evidence that the holy spirit is operating on them. Under the direction of the Governing Body, men who meet the Scriptural requirements are appointed to serve as elders or ministerial servants in the congregations. (1 Tim. 3:1-9, 12, 13) Those who meet the qualifications can be said to have been appointed by holy spirit.
*** cl chap. 16 p. 165 par. 19 “Exercise Justice” in Walking With God ***
19 Elders are often called upon to make decisions that affect their fellow believers. For example, elders periodically meet to consider whether other brothers in the congregation qualify to be recommended as elders or ministerial servants. The elders know the importance of being impartial. They let God’s requirements for such appointments guide them in making decisions, not relying on mere personal feelings. They thus act “without prejudgment, doing nothing according to a biased leaning.”—1 Timothy 5:21.