I am very worried about whether you would be in a better situation being married to him or not? So unless you have already had legal addvice on that, please see a solicitor as soon as possible in the next few days. If you didn't already have children with him I would just be saying like many others just throw him out - stay in your home with the children.
However, because the wedding/holiday is in two weeks, I think that you should just carry on as normal with him and get on that plane. If the solicitor advised you to marry him then go ahead and do that, and if you can bear it (I will probably be shot down in flames for this by Mumsnetters) have sex with him once after the ceremony, and not when he is drunk - but you could be a bit tipsy - so that he can't just get the marriage annulled. If this is out of date information (I am old) I'm sure that many on here will tell you, or ask your solicitor about that as well.
If the news is good in that you don't need to marry him for your and your childrens future security, then I think that because of the nearness of the wedding and the fact hat people will have spent a lot of money on it - as have you - don't say anything to anyone else about your intentions as the news would get out.
So go on your holiday, wear your beautiful dress on your 'wedding' day, walk down the Isle or stroll to the beach if it is a beach wedding, smile at everyone including the groom, and then when the marriage celebrant ask you if you will take your husband's hand in marriage, say a very gentle - but loud enough - sorry no, I can't, and then if you have the courage, and again staying calm, explain to everyone there exactly why you can't marry him.
If you can't face giving the explanation yourself, is there anyone on your side of the wedding party who can give the explanation for you, eg mum, dad, sister, brother, best friend, who you will have had to explain the situation to - maybe the night before?
I promise you that I am not normally devious or manipulative, and I also don't write for soap dramas on the TV, but this is the only way I can think of for you to still get the holiday, the reception party afterwards, and to wear your lovely dress.
By the way, if he wants to have sex with you in the meantime, you can tell him that you want to abstain now until the wedding night, in order to add a little more excitement to the "Day" itself.
Very good luck @Strawberrylatte at getting brilliant legal advice on what will be best for both your children and you, and for you wanting to follow through with it. 🍷🍸🍹