It would seem that both the mature young lady and the mature young gentleman must indubitably be Veneering's oldest friends.

Wards of his, perhaps?
Yet that can scarcely be, for they are older than himself.
Veneering has been in their confidence throughout, and has done much to lure them to the altar.

He has mentioned to Twemlow how he said to Mrs Veneering, 'Anastatia, this must be a match.' He has mentioned to Twemlow how he regards Sophronia Akershem (the mature young lady) in the light of a sister, and Alfred Lammle (the mature young gentleman) in the light of a brother.

Twemlow has asked him whether he went to school as a junior with Alfred?
He has answered, 'Not exactly.' Whether Sophronia was adopted by his mother?
He has answered, 'Not precisely so.' Twemlow's hand has gone to his forehead with a lost air.
But, two or three weeks ago, Twemlow, sitting over his newspaper, and over his dry-toast and weak tea, and over the stable-yard in Duke Street, St James's, received a highly-perfumed cocked-hat and monogram from Mrs Veneering, entreating her dearest Mr T., if not particularly engaged that day, to come like a charming soul and make a fourth at dinner with dear Mr Podsnap, for the discussion of an interesting family topic; the last three words doubly underlined and pointed with a note of admiration.

And Twemlow replying, 'Not engaged, and more than delighted,' goes, and this takes place: 'My dear Twemlow,' says Veneering, 'your ready response to Anastatia's unceremonious invitation is truly kind, and like an old, old friend.