Hi Peter,
there are no Eustons at all in Wales in 1881.
Looking for William Euston in 81 in England gave 9 results:
Select records to download - (50 maximum)
1. William EUSTON - Son Birth: <1876> Buxhall, Suffolk, England
2. William EUSTON - Son Birth: <1880> Clifton, Cumberland, England
3. William EUSTON - Son Birth: <1865> Derby, England
4. William EUSTON - Nephew Birth: <1879> St Georges E, Middlesex, England
5. William EUSTON - Head Birth: <1831> Aldgate, Middlesex, England
6. William C. EUSTON - Son Birth: <1880> Warwick, England
7. William D. EUSTEN - Son Birth: <1866> Harrow, Middlesex, England
8. William EUSTON - Head Birth: <1828> Egham, Surrey, England
9. William H. EUSTON - Son Birth: <1872> Egham, Surrey, England
We can discount no 1, 2, 3, 4, 6, 7 and 9
No 5 was a gun smith
No 8 was an ag lab. An Ag lab however, might have had veterinary knowledge, so I had a closer look. However he is married to Emma.
There are no Walton Eustons at all.
There are 6 Waltons in Wales, but all older than 9, so that counts yours out. Sorry I can't do any more. If you know where or when William was born I can have a look at 71 and 61 for you.
D
Have you got any certificates for the family?