Read all the threads op and glad your sister is seeing the light.
I'm a bit sad for her self esteem that she is already thinking on "who'd have her next.."
When really it sounds like she needs to learn to live by herself and find out what she needs in her life, gain some independance and not risk exposing her children to another controlling guy like this one. And focus on making herself and her children happy.
Perhaps along with the great support your family give her, she should get some counselling to work on self confidence.
It might be mirroring thoughts on what the DP might say to keep her in his life..."no one else would want you, I took you on despite all you kids from different relationships etc.."
Because it sounds like he's ruined her self worth.
Best wishes for the wedding, but still be on guard. He knows the venue, date and time...