Mistake on visa application

Hi

Need some advice with regards to my fiancés visa - For clarity we have applied, have been successful and my fiancé is in the UK with me.

Background:

My fiancé has a child which we listed on the visa application and triple checked everything to ensure that the name, DOB, everything was correctly represented.

A few years ago her brother had a child - which, incredibly sadly - Was an unwanted child. The grandmother (my fiancés mother) was devastated, never wanting to see one of her family in this situation, took on full responsibility for the child.

Issue:

We were collecting the certificate of no impediment the day before flying to the UK and the local government office mentioned to my fiancé as they were checking everything - That she had 2 children. Confused, she queried this and it turns out her mother used my fiancé's documents to register the above baby's birth in her name. She didn't want my fiancé to take on any responsibility, nor ever foresaw this being an issue, but she was not permitted to be on the birth certificate as the mother as she is too old.

Where we are now:

I have, calmly, raised an issue with her family about this, whilst all might be well between family, it looks absolutely awful for things like visa applications. We are:

- Asap (days or weeks) getting the child's birth registered to the actual mother, they are all still family and since some time has passed since the unwanted pregnancy, she is happy to have the birth certificate updated to correctly reflect her as the mother.

- In a mad panic about what this means for:

a) The status of my fiancés current visa. We have, like many couples I would imagine, invested a huge part of our lives into this and virtually all of our savings, what do we need to do if anything? I appreciate that from an immigration officers perspective this looks terrible.

b) The conversion to a spousal visa. Even if corrected, the second child may well show up on any historical records looked into. If not corrected on her current active visa, I'm at a loss as to how to explain this, short of deception to both my fiancé and I.

If this needs proper legal advice, unsure if specific firms are allowed to be linked, but we've put virtually all the money we have into just visa costs. If firms are allowed to be linked that are good value for money, reputable and/or knowledgeable in areas like this, I would be grateful.