Questions & Answers about Deras nya hemsida är faktiskt mycket märklig.
Why do we use the -a ending on nya but keep hemsida in its basic form?
This is a strict Swedish rule! After a possessive word like deras (their), you must use the definite form of the adjective (which usually ends in -a, like nya). However, the noun that follows it must stay in its indefinite form (just hemsida, not hemsidan).
Since nya gets an -a ending, why doesn't märklig?
Nya gets the -a because it is directly attached to the possessive deras. Märklig (strange) comes after the verb är (is) and is just describing the noun normally. Because en hemsida is a singular en-word, märklig stays in its basic, indefinite form.
Is faktiskt related to the English word "factual"?
They come from the same root, but in Swedish, faktiskt is a very common word that means "actually" or "in fact", rather than "factual".