Child dependants: Where should they live?

[tractorsponge]

I am due to marry my partner this year I am a British Citizien. He is American and currently is on a sponsored tier 2 visa. When he moved here initially he also had his wife and his son (now age 7) as dependents. As they have since divorced his ex wife is in the process of applying for a visa for herself but their son is still attached to my partner's visa. We are going to have to relocate to another city in the UK due to partner's job. It is a significant distance. At the moment partner and ex wife have a 50/50 custody agreement (not court ordered). When we move my partner would like to take his son with him, understandably his ex wife wants him to remain with her. Does their son need to remain with my partner as he is attached to his visa? Partner's ex wife doesn't earn enough to apply for her own tier 2 visa and is applying based on the fact her son lives here (this is what she has told us, I am not 100% sure of the details). What is the law regarding tier 2 visas and where any child dependants must live after a divorce?

[CR001]

If your partner changes his visa to a spouse Settlment visa, the child's PBS dependent visa will cease as the main pbs visa holder no longer holds that status.

Unlikely the mother of the child can apply based on the child if the child is not British. If they child has lived in the UK for 7 years and was born here, there is a route but it is a difficult one.

Has your partner officially divorced his wife?? You will need to submit evidence of the divorce. He was also required to inform HO that their relationship had broken down and was no longer subsisting.

[tractorsponge]

He was planning to just stay on his tier 2 visa until it was due for renewal (around 18 months) and then maybe change the type of visa based on our new marriage. He was going to look into this nearer the time and seek advice to what was best.

Their child is American also, born in the USA. I personally thought what she was saying didn't ring true, but as I am not an expert I didn't want to say anything. Their divorce came about as she had an affair (about 1 year ago) and now lives with her new partner. I am unsure if she is maybe applying for a visa down that route. Due to the nature of the break down of the marriage communication is strained and as such we only have the little information she volunteers regarding her visa status to go on.

My partner wrote to the HO to let them know when they separated and also when their decree absolute (UK) came through.