‘ Not sure if asking the PIL will help, one teaches and sees a lot of names so it could backfire! ’
As you say, one of his parents teaches & he has a traditional name, the PILs are more likely to think of the child at school & nix his ‘fantastic/gaming/esoteric’ names for several good reasons.
A workable outcome is that you may settle together on a short list of both your agreeable preferences & come up with a first & second name combination. The first name being one that your child can use (& spell) with ease & the second name as an a balance or compliment (not a compromise to a parent) to the first name. Once the child has grown, if they wish, they may choose the second name, or any other name, as their known name.
Which raises the question, why if your DH is so keen on these names, why does he not adopt one now? Just asking’ 😉.
As far as rocking up to the Registrars to name the child, although there are no UK laws about naming or naming conventions as there are in other countries, the Registrar may check or ask for confirmation that both parents present (or not) are happy with the names chosen.
As there are no legal grounds for refusal of a name, the questions about the name & agreement between the parents may be very clearly made. Once the name(s) are registered, it is an unusual & formal process to get the naming changed, hence the Registrars confirming that ‘unusual’ choices are a firm & agreed choice.
Although highly unlikely, if he tries to pull a fast one at the Registrars, make sure that you speak up at the time that you do not agree. You will be invited to go home, discuss & book another appointment when matters are settled.
Unusual, esoteric or obscure names may be interesting middle names, but as a first name it is not fair on the child.