How can I stop my relatives coming to my husband's funeral

Make it private funeral if you are questioned just say it was your husbands wish, sorry for your loss

Yes, Olivia, let them know that it is a private affair. It's hard enough arranging such an important funeral without having to worry about family fractures.
How likely are they to attend, just by seeing a notice?

My mum didn't want family except us at her funeral and made her wishes clear. I told family it was immediate family only and that was put in the newspaper notice.

Send your brother and sister a message saying that the funeral will be a small affair as asked for by your DH so they don’t need to attend, but that they can donate to whatever charity your husband preferred etc. Keep it simple and then leave it at that.
Am so very sorry for your loss and for the fact that your DH and yourself were not treated fairly by your brother and sister.
I hope you have other family members or friends who can support you right now.
😔

I think that your husband was still thinking of you., providing you with the reason to say no to them, as it is his choice, which as his wife you are following his wishes. They treated you quite badly and excluded you from their lives, so I think you could simply write to them or get someone else to speak to them and tell them that they would not be welcome at the funeral. The occasion is about you and the person in your life that meant so much to you. I hope that all goes well for you and that you are able to have the funeral that you want.