This is from my experience of dealing with prisoners and their families:
Some are completely cut off from their families. The family members may be victims, or horrified by the offences. Or just the person was an absolutely horrible person in family life and they don't want anything to do with them.
Some families stay in touch in a superficial way, but the prisoner doesn't realise this. It all comes out when the prisoner might be being released and it turns out their loving family were quite happy with them being in prison.
Some families absolutely believe in their relative's innocence. They stay in touch a lot. This is sometimes from cultures where family is everything, or family members who just can't believe their relative would do such a thing. When you meet the wives they are often vulnerable in someway.
Some families are just completely in on the game eg family with no obvious source of income, insisting on the relative's innocence while all the kids are in private school and the girls have ponies.
And some families are in touch because they have multiple members in the same prison.
Finally there are some fantastic mums out there, who totally accept what their son has done, but remain supportive, sensible, worry about their mental health and are just all round great parents where something (usually drugs) has gone horribly wrong.