Scene is not misspelled "Seene" in the Act 1 opening card. The lettering is done in Art Nouveau style. Several of the letters are embellished with decorative curlicues. The lower-case letter C in the word "Scene" looks almost like the letter E, but they are not identical.
The word 'being' is not capitalized in the opening title. However, as the title and acts "cards" are meant to reflect a theater's program, and theater programs are not immune to typographical errors, this should not be considered a Goof; in fact, it may be intentional.
At the end, it is not clear why Lady Bracknell's objections to the marriage of her niece Gwendolin to John (aka Ernest Worthing) would be erased by the revelation that John, in fact, was her nephew Algernon's brother. That would mean that the couple were first cousins, a fact that clearly did not seem to bother the two based on their cheerful embrace.
However, while marriage between first cousins is a contentious topic, in that era, it was not uncommon for first cousins to marry. In fact, it is currently legal for first cousins to marry in at least 20 U.S. states, Canada, Mexico, Latin America, South America, the United Kingdom, and many other countries.