aibu to say no?

No way. The mistake you. made was to give reasons, never ever explain, just say No, I can't do that. I am sorry, it sounds horrendous.

He needs professional help. Not a few days lying down. If he wants to detox, he should ask whoever prescribes the methadone. Also, he's 30... not 17, and really needs to take the lead in his own life. If the people pressuring you to do this, think its such a good idea, why isn't he staying with them? It's a hard family dynamic for sure. Maybe have a look at Families Anonymous, or Al-Anon on line. You all need support. 💐

What are they imagining, House MD-esque where you lock him in a bedroom with the windows locked for days until he withdraws? He could die depending on his current use, especially if he isn't taking his methadone as directed. It's dangerous and inappropriate.

Why aren't these family members sending him to rehab???

Just say no sorry it’s not going to happen

they either move in with other family members or find a rehab slot

"No sorry, I've got a lot going on at work and need my space. I hope he can get support from the GP and I'm happy to drive him to a dry clinic or pick up and drop off food and a prescription for him/whatever small support you want or can give. I can't house him. Speak soon xx"

He can then get in touch with local addictions team for support he’s looking for

I’ve always given people a home when they didn’t have one and people made me feel it was my responsibility and as a good empathetic socialist I did it because of my social conscience, I the space etc.

every single time I have done it I’ve been ripped off, used for labour, emotional support, had my hospitality abused in just about every way possible and I will never do it again.

protect yourself and your space. Addiction is complex as you no doubt know. Anyone withdrawing from any substance has the potential to be physically unwell, to be unpredictable, prone to mood swings or desperate behaviour etc, it is too much to ask of someone.
rehab centres exist for a reason, they’re not in someone’s home.
no GP or legitimate drugs worker would condone this abuse of your hospitality and kindness

YANBU. People don't kick a serious addiction of 3 years' standing in "a few days." He needs professional help and support not a brief stay with a well-meaning family member. Talking of which, why are you the one being pressured? Let one of the others take him in. It would be a firm "no" from me.

Your family are enablers - keeping him in the life

Without paying for rent,/mortgage/council tax/bills etc, he probably thinks he can spend even more money on smack

You are absolutely correct. Keep saying no

Absolutely NO !

People don't get off heroin 'in a few days'. It will turn into weeks/months/years with a drug addict who is just looking for free accommodation so they can spend their money (and probably yours) on more drugs.

If they genuinely want to get off heroin they need professional help.

No way. Not a chance. No no no 100000x no.

This, also don’t accept any pop in visits from
the guilt tripping family, as they’ll probably bring him and leave him!

Absolutely do not do it!!! Let those shouting about it help him.

jesus Christ no, he needs professional help and you’re not a professional.
Don’t put yourself in that situation.

absolutely no way. This will cause you a great deal of stress, it’s in no way fair for you to have to deal with his situation, unfortunately as it is, it’s simply not your problem. I’d also be concerned about the company he keeps and those people who might come knocking for any drug debt. You just protect yourself and put up boundaries. He isn’t going to manage to get clean just with a change of roof over his head. Suggest to the family he goes into a rehab programme

Why don’t they let him stay with them if they think it’s so necessary! Coming off such heavy drugs can be really dangerous and needs proper supervision and support.

What kind of family member are we talking here, because if it's your dad I would let him in if I'm honest

He needs professional help

You are being entirely reasonable to say No, @mycathasfangs. Are the people who are hounding you going to offer to house your brother whilst he goes cold turkey? I bet they aren’t!.

You should not be setting yourself on fire, to keep him warm, and the relatives who are badgering you need to wind their necks in.

Ask the ones pressuring you if they are so worried about the family member and so convinced that it's safe to have them there and that they won't sell household possessions for drugs then why don't they have the person living at their house?

I have no direct experience with your situation but I have extended family who have.
They tried to help but many things were stolen from their home to fund the addiction.
Absolutely do not trust that they won’t do this. It’s interesting that everyone wants YOU to accommodate them whilst ignoring your very real and valid viewpoint.
It would be a hard no from me, don’t give in to the pressure.