Fund requirements for visitor visa

Dear members
I am looking to bring my sister and her 9 months son to visit me for a month. I have been in the UK for nearly 10 years now and haven't had any family coming over.
I read the guidance but it is not clear for me:
1- How much money is needed to show as a fund? I know that it is not exact science and anybody needs to show how much they think it would cost per day plus tickets and etc. But when you apply for a schengen visa it says for example £40 per day. How much is norm to put aside per day for the UK?

2- her husband will sponsor her fully, but he is not applying for the visa. As he is on another trip at that time. Is it ok?

3- do they need to show the fund is in their account for a certain amount of time or just the transactions over 6-month period is enough?

4- my sister is not working right now. Is it ok if her husband shows his bank statement and saving along with a letter of sponsorship or the bank account and the money needs to be under her name?

5- is it better if her husband transfer the fund to her bank account and then provide a letter that he has provided and funded their trip and shows his bank statement as the proof of income or solely money in his account will suffice?

Thank you for your time

It's good that her husband is not applying. It means that her other half will stay in her home country. This gives her more incentive to go back. They always look at it this way: would the person have enough reasons to go back home once granted a visitor visa?

The money is a bit of a rocket science really. If you put too much they might refuse. I have seen a case refused because they told him the money he has for the trip represents a lifetime saving in his country and they don't believe that a genuine visitor would spend that money on a touristic trip over 10 days.

Don't move money last minute. It's better to show the availability over time which means that the money is genuinely available to the application. Moving money before the application is usually seen as an attempt to inflate the account and give a false representation of the financial situation. Someone from my family was refused just because of that.

If she is not working, she can show the money on a joint account with her husband. Not working usually carries a high rate of visitor visa refusal. You have to consider this option for her application.

Thank you for your kind reply.
Exactly. I do not know how much they need to show that is just right amount?!
Also, how long they need to provide bank statements for?
Thanks