Answer 1: That's the correct English translation of "Flan" as there is no "r" in Japanese, thus "Fran" Doesn't exist. Alas, his "Romaji Name" is Furan though.
Answer 2: It's really a matter of personal preference at this point.
In the official (not necessarily "correct" as translators can and do make mistakes) English translation of the anime, it's "Flan." On official (once again, not necesarily "correct") Japanese goods and merchandise such as trading cards, official artwork, etc. it's "Fran."
Both are official; neither are wrong. The Wikia chose a rendition and stuck with it for consistency.
Additionally, neither "r" nor "l" exist independent of each other in Japanese. The Japanese "r" is softer than the English "r" but harder than the English "l" and thus, the Japanese "ra-ri-ru-re-ro" sounds are used to immitate both "r" and "l" sounds in non-native pronunciations. This is a common confusion among English speakers doing Japanese translation and among Japanese speakers learning English.