There is no basis for a marriage of William Alexander to Catherine Wallace (abt.1625-bef.1680). Catherine does not even appear to be a family name.

Seven Brothers, Two Sisters: Ireland to MD Most researchers of this large group of Alexanders who settled in early Somerset County and the New Munster area of Cecil County, MD have believed that they were seven brothers and two sisters who emigrated from County Donegal, Ireland, to Maryland, with a possible stop in VA or elsewhere, starting about 1685.

Over the years, many researchers have attempted to identify the father of the Seven Brothers, Two Sisters, but none of the commonly mentioned candidates have been shown to be connected through primary source documentation. Before the American Revolution, descendants of the Seven Brothers, Two Sisters migrated to different parts of Maryland and into nearby Pennsylvania. Large branches also migrated to North Carolina in the same time period.

Family

https://www.wikitree.com/wiki/Alexander-2666#Children:__The_Seven_B...

The "Seven Brothers" have been identified by the now defunct website AlexanderDNA.org, replaced with FamilyTreeDNA, site as follows:[1]

1. William Alexander, b. cxa 1646
2. Andrew Alexander (ca 1648 - ca 1692/1700) m. Jane McKnitt
3. Elizabeth Alexander (ca 1650 - ca 1692) m. Matthew Wallace, born 1638
4. James Alexander 'weaver' (ca 1652 - 1735), 2 wives, both unknown.
5. John Alexander (ca 1652 - ca 1718) m. Mary Barbary
6. Francis Alexander (ca 1654 - bef 1701) m. Rebecca Unknown
7. Samuel Alexander (ca 1657 - 1733) m. Mary Taylor
8. Joseph Alexander 'tanner' (ca 1660 - 1730) m. Abigail McKnitt
9. Jane Alexander (ca 1665 - 1693) m. John McKnitt Sr."

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Catherine was born about 1625. Catherine Unknown ... She passed away before 1680.

https://www.wikitree.com/wiki/Unknown-202888

William Alexander, Sr./I was said to have married Catherine Wallis or Wallace. She probably was born in Scotland or Ulster, and died in Somerset County, MD. There is no documentation of this possible marriage, which is cited in some family trees. [At this juncture, it's best to say her LNAB is unknown. Later proof may still uncover it.][1]

• Reference: Ancestry Genealogy - SmartCopy: Mar 14 2019, 0:42:52 UTC

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• Reference: Ancestry Genealogy - SmartCopy: Mar 14 2019, 0:37:48 UTC