As you are a victim of violence in the home, and your partner was convicted of this, his Probation Officer should have outlined the risks he takes by contacting you. It could mean a recall for him if he breaches the RO. Also, his PO would have a duty to inform Children Services were you to be contacted by him.
In terms of you, were you supported by Victim Support during the court case? If so, Victim Support should be informed that he has been released from prison.
Also, should his post-prison supervision not be robust enough and you feel your child and you are at risk, you should contact your local IDVA.
His family would have to make an application to court to have contact with your child. As would he.
You have blocked his family from contacting you, that sends a strong message. If you feel at risk, call 101 and log a harassment once there have been more than two courses of unwanted action from them in trying to contact you. If two attempts of unwanted contact occur, that is an offence under the Protection of Harrassment Act.
You can call Women's Aid also free of charge for advice.
Stay strong, but please do tap into local support services. They are really worth their weight in gold.
I work with women leaving prison many of which are DV victims themselves, so te post-prison process should be handled by his PO. If he does make contact, please do ring the police immediately so the contact can be logged which should then go through to his PO.
Use what is available to you. It is vital for the safety of your son and you.