"You eat your dinner with us."
Translation:Itheann tú do dhinnéar linn.
The n in ndinnéar is not called an "n-prefix" in Irish.
The letters b, c, d, f, g, p and t are "eclipsed" in certain grammatical circumstances - one of those circumstances is after plural possessive pronouns ár (our), bhur (your) and a (their).
Each of these letters has a different urú, and words starting with d are eclipsed with n, so "our dinner" is ár ndinnéar, whereas words starting with b are eclipsed with m (bhur mbialann - "your restaurant"), words with c are eclipsed with g (a gcapall - "their horse"), words that start with f are eclipsed with bh (ár bhfón - "our phone"), g is eclipsed by n (bhur ngnó - "your business"), p with b (a bplean - "their plan") and t is eclipsed by d (ár dteach - "our house").
When the noun starts with a vowel, you do use an "n-prefix" - ár n-athair, a n-uimhir. But it is important to recognize that the n in front of ndinnéar is not called an "n-prefix". It's called "eclipsis" in English, and urú in Irish.