As a priest, I would have a few suggestions for you, BioNerd.
Over the course of my years, I have worked with families through issues that were painful…on both sides of the equation.
Parents who were disappointed in choices that their children made, on the one hand – whether co-habiting outside of marriage, marrying outside of the Church, having children outside of marriage, choosing to go to a different Christian confession, leaving the Church and faith all together – or realisations about their sexual orientation, among many other life circumstances.
On the other hand, I have tried to help people, with varying degrees of success, in dealing with issues related to animosity against the Church because of their childhood or some other aspects of their lives or families where they were wounded or damaged or pained on account of the Church.
All that by way of saying that I am sympathetic to the scenario you are presenting, regarding both generations in this portrait. I expect finding a mutual path ahead for everyone concerned will be a challenge for your brother and his companion, for you and your sister, and the others who are part of your respective lives as well as for your parents.
Not knowing any of you personally, it is very difficult to try to give you concrete and practical counsel, since advice really rests on knowing the people involved and being able to estimate their reactions, at least to some degree.
In terms of what you specifically ask in this post…
It would seem to me preferable for the matter to come out into the open in a planned as opposed to an accidental way since accidents can happen in unfavourable moments and unfavourable circumstance just as a realisation by a slow dawning could be awkward in the extreme and even tortuous.
It would also seem to me the occasion of a low-key small family gathering (and apart from a holiday) that you or your sister hosted in one of your homes would be better than at a dinner at a restaurant. A group of five is already substantial in a setting such as a restaurant when it is a normal occasion.
Rather than making the matter front stage, it seems better for the topic to come about in a more casual manner and without some dramatic build up, lest they think you are going to announce one of you is terminally ill.
Being in a non-public venue would allow your parents to not feel that they are trapped in the midst of strangers, as one can feel when one confronts something of great import while on a pubic stage like being in the middle of a restaurant. If they need space and time to process what they are told – that is if the matter really is a surprise to them that is totally unforeseen – they can make an early evening of it, without causing the disturbance of walking out of a restaurant, and return to their home…and your siblings and you will be together in a familiar place.
The other advice I can offer – and presume to do so since you are no longer practicing the faith and it might not occur to you – is the possibility of you meeting with your parents’ priest or a priest to whom they are close. Especially if he has been in their lives long enough that he might remember all of you from your younger days or have a particular closeness to them.
After this many years, there are a number of children from my old parishes who, having grown up, have chosen other paths in life – they know, however, that my door is always open to them. Similarly, for their parents…my door is always open.
Depending upon the pastoral gifts that the priest possesses, he may be able to offer the concrete suggestions to you that you are seeking on the one hand and also be available to help your parents process these realities and companion them as they process it on the other – and even know of a good counselor he could suggest.
I always counsel, on both sides of these situations, that the familial bond should in all cases be preserved. There are cases, of course, where it is tragically not possible at all, notably in issues involving some form of terrible abuse. Issues such as are being discussed here are not of that nature, thankfully, and should not be thought of as such. A way ahead should be sought and found.
A wholesale rejection of family members is always a tragedy, whatever side of the argument they are upon.
I can well imagine that the presence of you and others is a tremendous source of support and encouragement for your brother and I can also well imagine that, when he talks about this with his parents, who are your parents, too, he would wish to do so in the context of the entire family. As the one purveying news, that is his prerogative, after all.
It is evident in what you post that the children feel more affirmed by your relationships with each other than you do by your respective relationships to your parents and that the relationships of each of you to them is already a strained one. I am sure they must perceive that reality as well – and will understand it even more with the conveying of this news, if both of your brother’s sisters are sitting beside him.
I assure you and your family…all of your family…of my prayers.