Considering that our universe is only an estimated 13.7 billion years old and the solar system is "only" about 4.5 billion years old, a setting that's over 8000 billion years old is very... old. I don't think that you can really talk about "stability" on such time-scales and get a more meaningful answer besides "you're the author, so just make it so".

I meant stability when the planetary fusion happened not all the way to modern days, I just want to know if it was stable after the fusion and then I'll continue with the story.

I can't get past the mental block of an 8000 billion year old star. One can barley conceptualize the actual true age of the universe. An 8 trillion year time span is almost absurde. What even happens to matter on the atomic scale in 8 trillion years?

Now it's corrected, my apologies for the mistake and the confusion that I made.

We are lenient with new users, but for future reference please note that you area allowed one and only one question per post. Asking multiple questions is literally a reason to close your question. (See the "Needs More Focus" close reason, which is defined as "This question currently includes multiple questions in one. It should focus on one problem only.") BTW, you're asking nine questions. Note especially that some of the questions you're asking likely don't have answers. Finally, expect anyone who does respond to this post to not answer all of the questions as we're not obligated to do so.

@Antares "what are the results of such a system merge" violates the Book Rule. As much as I'd like to help everyone out by assuming they really have only one intent - that's not what happened at all. Stack Exchange is built around a simple model: one-specific-question/one-best-answer. And those answers are expected to be about one page long. Keep in mind I neither down voted nor voted to close - instead I explained to a new user what the expectations are. Please don't muddy the waters by rationalizing what for a more experienced user would be a clear reason to close the question. Thanks.

Tbh I had that same problem in my other post haha. Like F1cKrazy said: "Note that the rule is specifically about multiple distinct questions: it's permissible to have multiple questions as long as they're closely-related enough to be easily covered in a single answer." I think I've followed the rules @JBH . I know that this is complicated but I'll edit it and make it more easy to understand.

@Paleoaster3d If you want this reopened, you need to reduce nine questions to something considerably closer to just one that avoids the Book Rule prohibition. If you need help learning how to ask questions well on this Stack, please use our Sandbox. We're lenient with new users, but that leniency has limits and you're still expected to understand Stack Exchange's expectations.

I understand it, I'll try to reduce it and thanks for the help.

I reduced the answer and I made some diagrams for better understanding @JBH , I hope it helps.

Cheers. I voted to reopen. The only (minor) improvement I could ask for is that a line be drawn between each of the three conditions in your diagram to make it a bit simpler to see that you're presenting the before-and-after conditions for your question. If you get a chance, that would help. I'll also contact the mods and invite them to push the comments into chat so you get a fresh start. Well done.

What is the question? I can't see a question mark anywhere.

Thanks @JBH I'll draw that line and thanks for contacting the mods so I get a new fresh start.

@Ash the question is if this fusion would be possible and how it would affect my exoplanets.

I improved the sketches corresting some mistakes and giving a new text font and color besides adding the rings that I forgot to add, the Super-Neptune has faint rings so it's hard to see it.

@Paleoaster3d Please add the question in boldface to the end of your text for everybody to see

Sure dw, I'll do it now.

@Paleoaster3d: I have made some adjustments in the title and the question. Please check if you agree.

@Paleoaster3d: Also to add even more focus you could designate which planet's fate you are especially interested in (for example because there is life on it and is most plot relevant). Simulating all the planets might be complicated, but a rough plausibility check of the final system should be possible.

@Antares I agree with the adjustments, thanks. I put part one in the title because I'll ask several other questions about my worlbuilding (Mostly centered in the Kidnapped planet, the next question will be about the Brown dwarf). I'll add focus on the kidnapped planet because it's the most relevant to the plot.

I did some adjustments, I think that will be more than enough for now. Thanks for everything Antares and JBH.

@Paleoaster3d: Nice! Hope you get good answers now! :)

Thanks. :)