It was common practice to re-use a child’s name if one died. Keeping the name alive, literally. So two Williams, a few years apart, is very common.
Spelling varied all the time in Ireland. Beauconnell is more commonly known as Boconnell. It’s 175 acres and is in Seagoe civil parish. Looking at Griffiths Valuation for 1864 I see an Edward Lynch with a small 6 acre farm there. No other Lynches and no Fitzgeralds. It’s somewhere around Bleary though I can’t immediately find it on the Griffiths maps.
The variation in places of birth for the Lynch/Grimley children suggests the father was a labourer. They tended to move around to follow the available work. In contrast farmers tended to stay put. Labourers can be difficult to trace.
William Lynch’s marriage to Margaret Grimley was on 26.11.1830 in Magheralin’s records. The address given was Ballymakeown. Witnesses were John Houton (?) and John Lynch.
I don’t see the Fitzgerald-Lynch marriage in the surviving church records. They may have married outside Ireland or possibly in a parish in Ireland with no records for the 1850s.