Im a little younger than your mother. I’m so sorry love. Your story is making me cry. 
My upbringing was very much like this. My mother maintains to the bitter end that it was equal. But I wasn’t allowed to ask for boy fun things/toys and got to occasionally share my brothers stuff when I had prostrated and humiliated myself enough in his eyes. So he had a dog and I got dolls. Then when he was older, my father started to live vicariously through my brother. So for no reason other my father felt like it, he got a pony, a scrap motorbike and a succession of scrap cars to drive around my parents land.
I had to beg him to use them sometimes and I had to be ultra nice to him, which was humiliating as he was violent and bullied me badly both verbally and physically, which escalated into something worse in my teens.
When it was clear my brother was too allergic to the pony and my mother got fed up of caring for it, it was made very clear that the pony was too strong for me and they were selling it instead of keeping it for me/leading me round on it until I was strong enough. I am the younger child. Because it was my brothers pony, I knew my brother wouldn’t let me near it - he was the same with the dog so I never showed an interest in her even though to this day selling her digs deep in my heart. If asked, my mother would ridicule me and tell me I showed no interest in the pony and I’m making up stories.
Does any of this sound equal to you?
Your mother has set up a narrative, where she ignores anything, which doesn’t fit with her vision of herself. The way that she maintains the farce, that her children are treated equally is to pretend your marriage doesn’t exist. If you challenge her, she will treat you as an ungrateful child “after all I’ve done”. She will turn on you and make it very clear that when you actually get married the funds are available for your proper wedding, to a man obviously. She has no intention of giving you this money. £30 k is for weddings and you haven’t had one.
What would I do? For starters, I would stop playing her nasty games. You have been a pawn in her life for years. Consider writing a loving and caring letter to your entire family - aunts, uncles, grandparents etc. State in the letter you wanted to let them know you married your wonderful wife on x date and that you now realise how sad you are you didn’t get to celebrate your Union with them. Apologise for not letting them know, that you were told your wedding needed to be a secret and you didn’t have the funds for a big wedding. This would be the only way to put the situation out there for all to see.
Of course you don’t have to do this. And if you do, be very clear, your mother may possibly disown you and disinherit you. The entire family on both sides may also do the same. And your sister. Then there’s your father. Despite loving you very much, your father sounds like a weak man. He will do as he is told. So please,if you like this idea, do not go into this lightly or immediately. Take some time. Maybe years to consider if you wish to tell your family members. If you don’t wish to do it in such an open way, you could start by telling a cousin first perhaps and let it filter down that way.
Confronting your mother will do nothing. If treating you equally is brought up, you can tell your mother you know it isn’t true otherwise you’d be 30k better off. Be prepared for her to tear you to pieces. You will get nowhere by confronting her. The best way to do this is to write a letter. Rewrite it until you are happy that it is devoid of accusations and not overly emotional. Then either send it. Or keep it. Or burn it.
I sent my mother one such letter when I had just turned 20. But it was far too long. And she got nothing out of it except that I was a horrid and ungrateful child after all she had done for me. She disliked me even more after that. I also tried to speak to her when I was early 30’s. She got incredibly upset and I ended up backing down. I am mid 40’s and I now know she will never, ever look at who she is. And why? Because she is a narcissist and I am her scapegoat. She has projected all of her ill feelings about herself onto me. And I am everything bad. In confronting her with these feelings I was attempting to make her see herself warts and all. She is unwilling and unable to do so. Much preferring to let me carry the burden. I was always her emotional crutch as a child. From very young, I thought about her and what she wanted first. She was my world, and always on my mind. All I thought about was pleasing her - because it was so difficult to do, unattainable in fact. I put her on a pedestal and in in return, she favoured my brother. I refuse to be that person anymore.
We don’t get to choose our family. But as others have said, you have the opportunity to make a new family with your wife, close friends and people, who truly see you and love you for who you are.
What does your sister say in all of this? Is your wife invited to the wedding? If she is, it is also possible to out yourself at the wedding. “Hello uncle Jim, this is my wife, Tina”.