Theboysmum I am so sorry, this sounds exhausting and unpleasant, especially if your family are putting pressure on you.
"My family all disowned my sibling 4 years ago but now everyone is playing happy families again except me." Let the family do as they will, you choose if you want to see him, or let him see your kids. YOUR CALL.
"I have shielded my children from any sort of violence/ drug abuse because my mum was in a violent relationship when I was a child and some of my first memories are of violence. I want to keep my children innocent and pure for as long as possible but my family think I'm being unreasonable as apparently my sibling has now 'proven' themselves by staying clean for a whole 3 month."
You are not being unreasonable THEY are being unreasonable in questioning your own choices of who you want to associate with and who your kids should have contact with.
"I do admit to feeling guilty about this but probably because of the pressure they are putting on me." You need to stop feeling guilty, you are guilty of nothing. Is your mum, who allowed you to be exposed to violence also putting pressure on you? Maybe a few home truths that you do remember your early experiences that she allowed you to be exposed to! If she is not in the group putting pressure on you, maybe she could be an ally?
"I don't want my children to meet them and get attatched then lose that person because they've relapsed. " Very sensible.
"I'm so confused about what to do for the best I don't know if they are clean or not I only know what my family are telling me." I think deep down you are not confused you know deep down whether they have been clean for three months, or not, that actually you do not want your kids to have contact with your sibling, whether you do is up to you. If your family were not pressurizing you I feel quite sure you would know exactly what to do.
You can support your brother without giving him access to your kids, you know that.
Ginkypig I second that you certtainly "...don't sound like a snob."