"لَيْسَ عِنْد سيث تَنّورة."
Translation:Seth does not have a skirt.
for the name here it's simply how Arab people are likely to say a name like Seth because it is not an Arabic name they would probably pronounce it differently. Just like people in the UK might pronounce the name Muhammad as Moo-Ham-Mad whereas an Arab would say it slightly differently. Other than that pronunciation might change depending on where the speaker comes from which makes Arabic difficult to learn.
You might find helpful Aldrich, Arabic vs Arabic: A Dialect Sampler. In this case, see pages 92-93, which compares MSA (Modern Standard Arabic) or fus7a with how to say "I have" and "I don't have" in 14 dialects. My very limited understanding as a beginner is that you may be referring to that some dialects use معه (ma3a), "with" (Sudanese, Egyptian, Palestinian, Jordanian, etc) for objects, so "he has a dog" in some dialects is معه كلب. In other words, since Arabic doesn't have the verb "have" it uses "at" or "with" depending on dialect and context. Here's a link: https://arabiconline.eu/expressing-have-in-arabic/ I notice that Aldrich (p. 93) spells "you have" in Egyptian etc. with an alif: معاك
I'm a beginner, so no ability to fact check, but the following website makes a distinction: "In literary contexts, you may see ليس used to negate a present tense verb. For example, لستُ ادْري means 'I don't know' and is sometimes used instead of لا ادْري. This usage is rare today, but you may still see it in literary works and in poetry." http://allthearabicyouneverlearnedthefirsttimearound.com/p2/p2-ch1/%D9%84%D9%8E%D9%8A%D9%92%D8%B3%D9%8E/#:~:text=In%20literary%20contexts%2C%20you%20may,literary%20works%20and%20in%20poetry.