On the Father in law and husband thing... for one, it was mount Ephraim, I don't think the Levites name was mentioned (it took me a second to figure that out as well). On the calling him husband and father-in-law, Take the example of Bilhah, Rachel's handmaid. She is given to Jacob as wife in Gen. 30:4, but in Gen 35:22 when Reuben goes in unto her, she is referred to as a concubine again.
I know most dislike the Webster's 1828, but it is useful for such cases.
Webster's 1828 Dictionary [A-J]
concubine
CONCUBINE, n. L., to lie together, to lie down.
1. A woman who cohabits with a man, without the authority of a legal marriage; a woman kept for lewd purposes; a kept mistress.
2. A wife of inferior condition; a lawful wife, but not united to the man by the usual ceremonies, and of inferior condition. Such were Hagar and Keturah, the concubines of Abraham; and such concubines were allowed by the Roman laws.
David Clouds Way of Life Encyclopedia expounds similar:
Way of Life Encyclopedia
CONCUBINE
Wives of lower status than ordinary wives. Some O.T. men had concubines (Ge 25:6; 35:22; Jg 8:31; 2Sa 5:13; 1Ki 11:3; 2Ch 11:21). This was never God's will, though. It has always been God's will for one man to have one wife (Ge 2:20-25; Mt 19:4-6). God told Israel that kings must not have many wives (De 17:17). Those who did were disobeying God in that particular matter, even though some were godly men. David is a key example. He multiplied wives to himself in spite of God's command against this, but his lust also brought him into terrible grief.
Next:
American Tract Society Dictionary
CONCUBINE
A term which, in modern authors, commonly signifies a woman who, without being married to a man, lives with him as his wife; but in the Bible the word concubine is understood in another sense-meaning a lawful wife, but of a secondary rank. She differed from a proper wife in that she was not married by solemn stipulation, but only betrothed; she brought no dowry with her, and had no share in the government of the family. She was liable to be repudiated, or sent away with a gift, Ge 21:14, and her children might be treated in the same way, and not share in their father's inheritance, Ge 25:6. On cause of concubinage is shown in the history of Abraham and Jacob, Ge 16:16.
Hope this helps.