Testing Siblings and other close family
This is worthwhile. I was sceptical about this at first because kits were so expensive and originally my goal was to work out what was happening back in time. However, testing close relatives can be useful, especially with the oldest relatives you have.
It proves they are all related in expected ways.
It will provide your own bank of known DNA - a reference system to use later. Anyone matching a known relative can be tracked to a branch of you tree.
Identifying parental DNA is also useful
For establishing which side a DNA connection belongs to.
You can identify genes on your mothers side and your fathers side - halving the issue of how you match with a new contact
Also identify ethnicity on different sides or parts of the family.
Your children and later generations will benefit from testing because, in a few generations, they will eventually lose their DNA connection to your ancestors.
All members of a distant family will not match
A correspondent’s mother matches me and two of her sisters match me, in similar ways and one brother in a different match. Another brother provides no match at all. This is the normal way that DNA is ‘randomly’ donated to children. Each child will receive a different set of gene mixtures that makes them different from each other.
Ten percent of fourth cousins can not find a DNA connection?
Where a parent is not available, uncles and aunts can be a form of substitution but bear in mind the comment above that brothers and sisters are not clones of each other. Instead of 50% of your DNA being similar to a parent it will be somewhere around 25%,or less but at least you know which side of the family it comes from (unless there is cause to believe that your parents have ancestors in common).
New techniques are coming along where you can re-create DNA of ancestors (currently parents and, maybe soon, grandparents from childrens DNA - the one drawback seems to be, ideally you would have 8 children tested!!!
Equally, you can now find the non-common DNA and start to identify this with known surnames which helps identify more distant DNA relatives.
Seamus Crowe. Website2021