All I can offer is what is available inLedyard Bill's 1867 compilation of the Bill family. James Bill, is enumerated as the 95th Bill on page 127. He was the descendant of Samuel, Philip and John. Samuel's wife was Mercy Haughton, daughter of Richard Haughton of New London. At some point after bearing eleven children she apparently died as Samuel's will recognized Elizabeth as his wife, no further information on her being offered. James was the 4th child of Samuel and Mercy and was born about 1694.
As you note, James Bill married Mary Swodel. She was the daughter of William Swodel, of Groton, CT, and the sister of Hannah Swodel, the second wife of James' uncle Joshua Bill. After their marriage James & Mary were found in Lebanon, CT with his father and many of his family. In 1719 they purchased a farm in Hebron where they appear to have lived for some years before returning to Lebanon. At some point in the 1850's it appears that James moved to Wantage, NJ with his son James and, possibly, Jedediah as well.
Again as you note, Mary is listed as having been born 2 July 1721 BUT it is further noted that "She or her sister Experience m. Joshua Eells". I leave that one for you to trace further as no more is given for either woman other than Experience's birthdaate of 10 October 1724.
As far as Joshua becoming a Loyalist is concerned I must ask whether it is correct to state he "became" one or simply was one because he was in Nova Scotia at the time of the American Revolution rather than in one of the thirteen colonies. A fine point, perhaps, but I believe it is an important distinction none-the-less as I have never heard of any agitation for revolution coming out of the Maritime Provinces at the time of our own revolution.
Hope this is at least of some help to you if you have not already viewed Ledyard Bill's book and would be interested in anything more you might have on Mary, Experience or their ancestors.