I don't know about the other Allen but Abigail Allen was the daughter of Samuel Allen b. 1598 d 05 August 1669 Braintree (now Quincy) Massachusetts m. Margaret French.I have a brother for Abigail, but no other sisters. incomplete.Margaret French also married Edward Lamb.
Samuel Allen's other wife was Anne Whitemore.Samuel and Anne had a Sarah b 30 March 1639, but she married Josiah Standish in Aft. 07 March 1655/56 as his second wife.He was the son of Myles of the Mayflower.This Sarah would have been half-sister to the Abigail Allen above.