What Julian is feeling is the pleasure of a task well completed -- his emancipation, and the uncertainty of the future and the hard work ahead. Sam's presence would help.
While your last sentiment regarding Julian's brother would be welcome, I don't think the father will be keen to lose his second son, particularly after he reads the letter from Julian.
Excellent chapter. Can't wait to see what the Barnswallow and Wardell farms look like. My only negative thoughts were about how long they kept Runyon waiting out in the yard.