Hi BumptiousandBustly
I think how you proceed really depends on whether your goal is low contact or no contact.
Low contact is to send and receive birthday cards etc and do duty visits as necessary.
I did this for years but am now no contact.
For no contact - it really is what it says no contact.
I sent a no contact text and did not reply to any further communication from my parents.
I have changed my land line and mobile telephone numbers. I only have one impartial relative who has these numbers for emergencies only - but tbh I can't now imagine any emergency that would make me want contact again. (Caller ID wasn't sufficient to stop silent calls and even seeing their number would send me into major anxiety mode...so new numbers solved that one).
I don't do facebook and neither do my DC's or DH - so no problems there.
I haven't sent any Fathers Day/Mothers Day or Birthday cards this year and can't see me sending any in the foreseeable future.
My parents sent Birthday cards to my DC's (they are pre/teens)...they had guilt trip messages in them - I opened the cards with my DC's permission before they saw them...told them the cards had messages in them designed to use my DC's to guilt trip me into visiting. I asked them if they wanted to see/have the cards anyway, they said "No, put them in the burning pile with the bills." Rather than do this my DH has hidden the cards where I can't find them and we have saved them as 'evidence' should we need them in the future to explain my no contact decision to the DC's.
If any gifts had turned up then I think we as a family would have taken a trip to the local children's ward and dropped the presents off there.
How did I explain things to my DC's in the first instance? I was basic and honest, bearing in mind they had already seen my parents kicking off in my house and they are all 10 y/o+ so not saying anything isn't really an option.
Along these lines....
Mummy has a difficult relationship with Grandma and Granddad. Grandma and Granddad like things done their way and their way only...there are no discussions allowed...if I try to discuss my opinion they will tell me I am being silly and to be quiet. This makes Mummy feel as if her opinions and thoughts don't count - which makes Mummy feel very unsure about herself, so to allow Mummy to be confident and happy then it is better for Mummy not to be involved with Grandma and Granddad.
I then asked they DC's how they felt about things and did they feel the need to visit Grandma and Granddad by themselves - they all said that as they didn't have much to do with Grandma and Granddad anyway, that if they did visit they wouldn't feel that they had anything to say to them.
I have always kept a good distance between my parents and my DC's - parents have never baby sat or had my DC's for tea etc so there wasn't much of a relationship/connection to disrupt.
Since then they have asked questions about my childhood such as did Grandma teach you so and so? To which my reply has always been a flat and unemotional truth...no she didn't, she was too busy doing other things...it was your Great Grandma that taught me this.
I think they have heard me talking to my DH about stuff also and they asked whether I got smacked when I was a child again I was honest but brief. "Yes, if Grandma and Granddad thought I had been naughty I was smacked." (It was far more than smacking - but to tell them all the facts I think is too much for now).
As for school...I just telephoned and had my parents removed from the contact list. I said there had been a change in circumstances and to remove the names please.
As for what I tell other people...generally nothing...tbh here is only place I 'talk' about them...otherwise a "We don't get on..." seems to suffice.
I don't know if any of this helps or is perhaps a bit too far for you, but this is how I dealt with no contact.