Hi Owenthomas, and welcome to RootsChat,
Assuming the family at Tyddyn Hwrdd, Llangeinwen in the 1881 census are your relatives
I have found the following in Anglesey BMD records which refer to them.
Birth registrations:
Ann Ellen - dau of Owen Jones and Mary Roberts, born 9 Jun 1874, Llangeinwen
Mary Anna - dau of Owen Jones and Mary Roberts, born 31 Aug 1870, Llangeinwen.
Deaths (all at Tyddyn Hwrdd, Llangeinwen):
Ann Jones, age 6 months, dau of Owen Jones - 7 Jun 1852, labourer. Informant Owen Jones.
Catherine Jones, age 11 months, dau of ostler & car driver Owen Jones - 7 Mar 1877. Informant Mary Jones, mother.
(male) Jones, age given as 5 minutes, son of agricultural labourer Owen Jones - 24 Sep 1868.
Mary Jones, 50, wife of agricultural labourer Owen Jones - 20 Jul 1882. Informant Owen Jones, widower.
Owen Jones, 18, son of agricultural labourer Owen Jones - 16 Aug 1867. Informant Mary Jones.
The following also died at Tyddyn Hwrdd and perhaps are earlier generations?
John Owen, stonemason, 68 - 18 Aug 1865. Informant John Jones, Pendref, Llangeinwen.
Mary Owen, widow of stonemason John Owen, 66 - 20 Apr 1866. Informant Margaret Hughes, Dwyran, Llangeinwen.
Owen Jones, farmer, 85 - 2 Apr 1845. Informant Owen Owens, Melinwen, Llangeinwen.
I have looked for the birth registrations of Owen Jones' other children:
Catherine - dau of Owen Jones and Mary Roberts, born 30 Mar 1876, Llangeinwen.
(male) - son of Owen Jones and Mary Roberts, born 24 Sep 1868, Llangeinwen.
The other two children were from Owen's first marriage:
Ann - dau of Owen Jones and Elizabeth Griffith, born 22 Dec 1852, Llangeinwen.
Owen - son of Owen Jones and Elizabeth Griffith, born 22 Dec 1848, Llangeinwen.
Marriages:
I can not find the marriage of Owen Jones and Mary Roberts - given Mary's place of birth they may have married in Caernarvonshire?
I can find a marriage between Owen Jones and Elizabeth Griffith(s) but it was at Llanfair Mathafarn Eithaf, near the east coast of Anglesey and some distance from Llangeinwen:
Owen Jones, full age, bach., labourer of Dafarn Tywysog, son of John Owen, stonemason married Elizabeth Griffiths, full age, spin. of Tanydinas, dau of Edward Griffiths, labourer on 11 Jan 1848. Both signed by mark, the witnesses were Jonathan Thomas Evans and Griffith Griffiths.
Finally there was a death at Llangeinwen, but not at Tyddyn Hwrdd, as follows:
Elizabeth Jones, age 39, at Minffordd, Llangeinwen, wife of agricultural labourer Owen Jones on 4 Nov 1858. Informant Thomas Evans, Lleinian, Llangeinwen.
Hope this helps.