there are various different DNA tests that tell you different things (are you legitimate, or whether you're a Neanderthal for instance) - you might need to consider exactly what you'd like to find out from a test.
Remember, we share 57% of our genes with cabbages!
oh, and to start, write down the names and if possible dates (birth, marriage, death) of every relative you know. Ask your relatives if they know about more relatives. Try to do it soon, before they're all dead and can't tell you anything - a common problem with family tree builders who don't get going till they realise all the older generation have gone.
One reason for two birth registrations is that a child died so they reused its name for a second child. That doesn't happen so often now as child mortality has been greatly reduced, but a century or more ago it was very common
Were the child's parents married at the time of the first birth registration? If not, a later registration of the birth (after they'd got married) might have been sought in order to avoid the stigma associated with bastardy.
You can buy credits to view the information you wish to see.
Mrs JtH is Scottish and you are in for a real treat doing research using Scottish BMD Records.
They give you so much information far more than an English ones.
A Birth Certificate not only names parents but gives date and place of their marriage, etc.
https://www.freebmd.org.uk/ is free but I'm not au fait with how much Scottish data they have. If none then why not contact them and suggest they could do so ?
I don't think one can view actual BMD certificates on line. The ones I bought were all serial numbered, I suspect authorities like to know who's accessing such information.
Your explanation that you are Scottish/Irish with possible Spanish blood mixed in reminds me of someone I knew. If you were adopted then were you by any chance born in the 1966-1968 period, do you have any connection with the Perth/Tayside area ?
While Scotland is possibly an easier place for finding information than is England, the UK as a whole is sadly quite a difficult/poor place to go about this sort of thing compared to other European countries, particularly the northern ones.
I once tried one of the DNA tests, and I was disappointed. It gave me a general overview of what it said was my ancestry, but it consisted only of maps and statistics of population movements over millions of years. I had hoped for information that was more detailed and relevant to me, but that didn't happen. That was a waste of money, as far as I was concerned.
I`ve just found out I have a relative who was a lunar rock scientist at NASA through Ancestry DNA. His Mum told me and I found her because we share similar DNA which is the most interesting part of having it done - you can find your near matches. As more people get tested there will be more matches that pop up.
237SJ, I've been notified of several third or fourth cousins. They seem all to be housewives in Minnesota. As far as I can see, there's no way I could be related to any of them.
bookbinder, you have to be careful which test you choose. My OH took that one (a mere 1% Neanderthal, which is less than average) but you obviously want to know something completely different.