How Do Families Reduce Re-Offending?

Supportive families of prisoners can reduce re-offending? And what about the prisoners with a substance abuse problem? In addition to that; how do we support a loved one in prison when the prison's are awash with legal highs and other addictive substances? 
How do supportive families reduce re-offending? 
When I send money in to a prisoner for telephone credit so he can ring his family; how do I know if that money is purely spent wisely - and I mean wisely in the sense of phone credit and essentials from the prison canteen? 
The problem I have is; if a loved one is an addict; by me sending money in; is only enabling the prisoner to pay for drugs inside. 
The fairy-tale is wonderful; man comes out of prison completely clean of drugs, gets a great job and becomes Dad of the year. It's a fabulous ending to a prison journey - but how many inspirational endings are there?
Maybe I will receive an endless flow of emails and stories that would prove me wrong - I shall wait for them. 
I was talking to a lady who had the success story. She supported her partner for 8 years and he was 4 years clean off drugs. He was doing remarkably well; had a job, a nice home to live in and bonded well with his children when he was released from prison. A few months ago he relapsed and has lost everything again. 
His partner is devastated, his children are confused and the road he is walking on has a prison at the end of it. 
Will his partner support him all over again if he inevitably goes back to jail? 
Right now, her answer is no, because a drug addict, especially those using class A drugs, usually relapse time and time again. It is exhausting being around an addict and it is mentally draining being their 'carer' whilst they serve a prison sentence.
It's all to easy and flippant for the government to say families are the key to reducing re-offending. It's a load of misleading crap. 
There is no doubt there are success stories, I have read a few myself, but the success stories involve ex-prisoners who aren't drug addicts. 
We need to evolve here and say - Supporting prisoners families with a loved-one/drug addict who is serving time in prison. 
The only time you can support an ex-offender/addict upon release is if they go straight to rehab.