Well, here it is, the finished product, enjoy!
Disclaimer: I own nothing to do with 'Pride and Prejudice' that is in this story
After the wedding ceremony, the guests gathered back at Longbourn for the joint wedding breakfast to celebrate the two marriages. Many of the friends and family of the four had gathered to provide the good wishes to the two couples. In the midst of the festivities, across the room Mrs Bennet saw her elder son-in-law across the room, and felt herself obliged to establish herself as a maternal figure "Well, Fitzwilliam" for now, she was entitled to addressing him by his Christian name, "that was a delightful ceremony." Silently, Mr. Darcy groaned, finally fully grasping that he had now gained not only Elizabeth, but the whole family in the process. "Yes, Mrs. Bennet, it was." was his reply to her, not wishing to use a familiar term to address his newly acquired mother-in-law, and quite possibly encourage her in the process.
This was of course, not the response that Mrs. Bennet had had expected, for she felt it only right that a son-in-law address his mother-in-law by a more familiar manner, and she felt it was her duty to make that very clear to him. "Now, Fitzwilliam, we are family now" making it clear how pleased she was about this fact, "and it is only right for you not to be quite so formal now, of course." And completely ignoring any opinion Mr. Darcy may have had, continued "now, I expect to receive an invitation to visit my dear Lizzy at Pemberley soon, of course, as she simply must need some help in the running of such an estate as Pemberley."
"I am sure that she has learned perfectly fine to run the estate Mrs. Bennet. I am positive that she will do just fine in the running of it without you making the journey in going to Pemberley." Was his response, in an attempt to not extend Mrs. Bennet's desired invite to his estate.
Almost as if Mr. Darcy had not given a response to her, she continued 'It would be such a comfort to Lizzy to see her family again, and of course I couldn't bare to leave behind Kitty and Mary.' Pausing for an instant, once again not giving a chance for Mr. Darcy to voice an opinion, his silent reproach at what Mrs. Bennet was suggesting, she went on. 'There's a very good idea now, Kitty and Mary would make such good friends for your dear sister, wouldn't they Fitzwiliam? My girls are not too much older than she is, and would be such good examples for her.' giving another pause, to make sure that Mr. Darcy was still listening to her, oblivious to his concealed horror at not only the very thought of Mrs. Bennet being at Pemberley, but also two of her daughters, his horror only continued to grow as she apparently had another thought. 'Oh, and indeed dear Lydia hasn't seen Lizzy in such a very long time, she simply has to come along as well, and it is simply not right for a lady to leave her husband, for any amount of time, unless he is already away on business or otherwise, so of course Mr. Wickham will absolutely have to come with her.
Mr. Darcy, looking around the room, looking as proud as ever, was hoping to find a way to get away from the conversation he had been unwillingly pulled into by the horrifying woman in front of him, and trying to find Lizzy in the room full of people. He merely acknowledged the woman's comment with a cold look, and tried to not look too affronted with the thought of not only more of the Bennet family in his estate, but at the mere thought of Mr. Wickham there as well.
As the conversation was happening, Mr. Bennet and Lizzy had made an approach towards them while holding their own conversation, and Mrs. Bennet turned toward Mr. Bennet, asking him in vain to make his desire known to visit the Pemberley estate, and visit Lizzy and to make absolutely sure that she knows exactly how to run an estate like Pemberley. "Now, now, I am sure that they will extend the invite soon enough," was his remark to her "and soon enough we shall be visiting."