One of the reasons my family tree is so enormous is I’ve researched the siblings of my direct ancestors, and their descendants. Researching 2nd, 3rd. etc. cousins can help solve identification problems, as well as unearthing interesting stuff.
Just how useful it can be is being brought home to me at the moment, as I’m researching my Logan line in Aberdeenshire. My gg grandmother Mary Logan was born in 1838, the daughter of John Logan and Isobel Booth, so I’m heavily reliant on the Old Parish Registers to go further back. But given her birth date she’d have had relatives in the census and who hopefully managed to wait until after 1855 to depart life and so have a death certificate. Looking them up has helped me piece the Logan family together: if I’d focussed only on Mary’s parents, grandparents and great grandparents I wouldn’t have been able to reliably prove a connection and would have missed out on interesting detail.
Also of enormous help was looking up baptism records in the OPR via ScotlandsPeople and not just relying on FamilySearch. Mary’s baptism told me that her father John Logan was from Auchtilair in the parish of Old Deer. Looking up Auchtilair on an old map showed it to be south of the village of Stuartfield and next to Creichie. John Logan died before official registration but he and his family are in the 1841 census at Auchticlair, and accessing this on ScotlandsPeople showed a Jane Logan living next door. The census also showed that John had children born well before he married Isobel Booth: researching William Logan, one of the older children, produced a death certificate from 1858 with his parents named as John Logan farmer deceased and Ann Logan ms Simpson deceased. There was an Old Deer marriage for John Logan and Ann Simpson in 1829. So John Logan was married twice, Mary’s mother being his second wife.
I then went looking for the birth of a John Logan who was old enough to have married in 1829, and found a baptism in 1796 in Old Deer for John Logan, son of James Logan and Catherine Smith, plus a marriage for James and Catherine in 1789. I then looked for their other children and researched them: the second child Jean (or Jane) Logan turned out to be the one living next door to John at Auchtilair in 1841. From 1851 onwards she lived in Stuartfield, the nearest village, and died there in 1878. Her death certificate gives her parents as James Logan crofter and Catherine Logan ms Smith. Jean/Jane also had living with her a niece Jane Logan, who was the daughter of John Logan and his first wife Ann Simpson. So that all nicely proved that my ggg grandfather John Logan had two wives and was the son of James Logan and Catherine Smith.
There’s more to research for my Logan of Aberdeenshire line, of course, but including siblings into the research has really helped.