You're both named on the lease, I assume. If not, you'll need that permission from the landlord.
For the cash savings, I see two sources: IRAs and mutual funds? For the IRAs, what date does the November statement begin and what date does the April statement end? Do you have six FULL months? For the liquidated mutual funds, do you have a statement that shows you held them for six FULL months and a bank statement showing the proceeds of the liquidation going into an account that you currently hold?
Edited to add:
I just saw your questions at the end!
Questions
1. "Evidence of where Miss XXXX's other parent lives - such as utility bills". Our 2 children both have UK/US citizenship so they are not on the application. Do I need to provide anything here since I have included statements under correspondence above?
2. My IRA statements are addressed to my mother-in-law's address in the US because we don't want them to get lost. Will this cause any issue?
3. Do I need to provide our prior lease or just the current one (even though some correspondence is addressed to the prior flat)?
Thank you very much!
1. I don't know what evidence is required for children. Is the daughter in question from a different relationship? That might be relevant to whoever comes along to answer this question.
2. The address on the IRA statements won't be a problem unless you're using them for your items of correspondence... but I see that you're not.
3. Just the current lease. You need to show that if they approve the visa, you will have someplace to stay.