Applying to HMRC for Child Benefit for one of my two kids.

Hello folks, hopefully someone will be able to help with this query. It's a bit off topic being about Child Benefit rather than Child Maintenance. 

My ex split (not married) with me in 2019 and things got fairly toxic around the point she took legal advice and my dad dying (leaving me with some cash) about 9-12 months after the split. I won't go into all the details for brevity but it was really horrible with lots of very nasty attacks on my character, lots of lying, hypocrisy and manipulation of me and the kids by her to get as much out of me financially as she could. She took me to court in the end and I won 5050 custody of my 2 kids, basically because CAFCASS were impartial and I could easily prove that her allegations against me were lies.

But what I'm looking for is advice about how best to collect evidence and how to present it to HMRC to try and have the child benefit split (1 child each) between me and my ex. Luckily she hasn't made a claim for Child Maintenance, because she lost the court case, because I pay her more than she would get (I currently work part time and have a low income so would pay minimal amounts) and because I think she may have committed benefit fraud to obtain Universal Credit and she is likely worried I will let the DWP know if she tries to make me pay her CM.

Details of possible benefit fraud. Any ideas if this is actual fraud?:

My ex asked me (via email) to take my name of CB in late 2019 as she said she would be able to get more money for the kids if we did this. I agreed to do it as was trying to keep things amicable and still trusted her, but was expecting the payments to still go into the joint account. However she kept the money and used it to start a claim for Universal Credit and to move out of the family home into a flat with rent etc paid for by UC.

At that point my dad was very ill and I had already arranged to live near him to help care for him and I asked my ex to remain in the family home so I could do that. I was in a flat nearby our family home at the time so not really living there. My dad lived about 40mins away from our family home so it wasn't too impractical. My ex refused my suggestion and stated she could get UC if she moved out (via email/messages). I think this might be 'deprivation of capital' as she never needed separate accommodation paid for by UC. She moved out and i stayed in the family home and my dad died a month later.

I had always stated that I would be happy to buy the family home. It needed lots of work and I saw it as a long term investment that my skills fit with and we had it recently valued as part of a negligence case. My ex didn't like the house as it was a mess. During the time I was trying to buy her out we were going through a legal negligence claim against out surveyor from when we purchased the family home in 2016 and we couldn't do work on it to spruce it up. My ex repeatedly delayed the sale of the house to me and admitted in an email that she was 'trying to make the sale to me align with the pay-out from the surveyor otherwise she would lose access to benefits'. I have other evidence of these delaying tactics, like I was offering her 60% of the shared asset value but she kept refusing to sell. I think this is also evidence of 'deprivation of capital'.

After my dad died I offered to move into his house so I could get it ready for sale, and to enable her to move back in and stop claiming as much Universal Credit. She obviously didn't want to do this.

Would giving this evidence of her trying to maintain access to benefits help my case? Not sure I want to risk the damage this may cause unless it's likely to work.

Currently I have the kids half the time (written in a court order) and pay for 50% of the kids essentials, such as school trips school clothes stationary etc and some of the extra curricular activities that she has organised. I also pay for all the kids rabbits costs so I don't pay for half of one of the activities she does to balance that. I do most of the kids doctors trips as they tend to fall on my days and I have a car, she doesn't have one. I could easily survive without a car but use it primarily for the kids. My ex changed all important addresses when we split to hers but I do all the important meetings with school and doctors as much as she does. I've not historically bought as many clothes for the kids as my ex, as she originally said she would pay for these but i'm paying more and more as time goes on. I pay pay pocket money of£40 a month and my ex puts a similar amount into a savings account for them instead. She does pay for both kids phone's I used to pay for one of them but she gave my son a much better phone so he didn't want the one I provided anymore. My ex earns significantly more than I do and simply uses up the CB and then asks me to match her costs, that are essentially what HMRC are covering via the CB. 

I've just changed banks and forgot to download all my old statements so probably need to wait 12 months before I make the application to HMRC with evidence. So I have time to plan this if I need to. Any advise would be very helpful. Has anyone had any success doing this?

Many thanks!