Hi mummyjen2
Consider very carefully why you want contact at all; if its just to assuage your own guilt here then its really not a good enough reason to restart contact. You seem very much in a FOG state still as it is; you need to break free of the fear, obligation and guilt re them.
Do you think either of your parents here feel any guilt; I doubt that very much so why do you feel guilty at all?. Abusers can be "nice" sometimes but its only on their terms and it never lasts long. Its all part of the nice/nasty cycle of abuse and that is a continuous cycle. This has nothing to do with what culture you grew up in and or nationality; abusers are of all colours and creeds and operate on a power and control basis. This is what abuse is about; power and control. They still want to wield that over you and in turn your own family unit.
I can understand why you are feeling guilt; this along with fear and obligation are some of the main legacies that such toxic abusers like your parents leave their now adult offspring.
No contact however, is precisely that. You need to remain no contact; any contact at all with your parents will put you straight back to square one with your children, you and your H being abused too by them. They were not good parents (understatement) to you after all, these people have not fundamentally altered since your early childhood.
People from dysfunctional families end up playing roles; what is your role here?. You seem like the scapegoat for all their inherent ills with your sister perhaps being more favoured overall. She seems to be enmeshed unhealthily with your parents and she is being unfair by asking you to attend her wedding particularly if your parents are going to be there too. Its too much for you to cope with so I would not attend. Your H may well think that he is trying to protect you from your own self here because he has seen all too clearly their abuses of you and his family .
You really do owe your parents nothing given their abusive treatment of you. If you really do not want your children to go through the same thing then you need to stay no contact. What do you think contact would achieve anyway; once opened that Pandoras Box is bloody hard if nigh on impossible to get shut again. Any boundaries that you care to impose on them would be roundly ignored and they certainly are not going to say sorry or apologise for their actions. They honestly feel they have done nothing wrong here. Its not your fault they are like this; you did not make them this way and their own families of origin did that to them.
I would look at the website entitled Daughters of Narcissistic Mothers and contact NAPAC (who are an organisation for people abused in childhood). napac.org.uk/ You also could do with talking to a therapist who has vast experience of dealing with abuse and narcissism hence the suggestion too of contacting BACP.
You may also want to post on the "well we took you to Stately Homes" thread on these pages and read the resources at the start of that thread.