All credit goes to Brother Landers for these observations. I once asked for his thoughts on Ruth 1:8-9, and this is how he replied:
Well, since everybody else goes lazily with the stale "May [YHWH] grant..." perhaps the brothers wanted to make a more inclusive, vibrant, or "amplified" translation, embracing the various facets of meaning behind the verb *n-t-n*, i,b
The NWT has been accused of many things, but never can it be accused of being "stale." :-)
The verb and its derived forms sustain "a great variety of meanings" according to the Hebrew lexicons, with three broad areas of meaning: 1) give, 2) put or set and 3) make or constitute. TDOT gives the elemental meaning "extend the hand" in order to place an object at a specific place or to give it over to another person. One Jewish etymological source says the basic idea is simply to "give over (something)."
"May Jehovah make a gift to you" of a resting place with a husband is the thought. It's more expressive and contextual (since it would be a gift, indeed) than just "grant," and is a legitimate translation.
[It's interesting that the 2013 revision of the NWT now says: "'May Jehovah grant* that each of you finds security* in the home of your husband.' Then she kissed them, and they wept loudly." The wording "make a gift" now appears in the footnote.-EGF]