This is the 7294th most frequent Russian word.
выглядят
"Look" or "appear" (plural form).
Here, 'выглядят' describes the observable characteristic of the flowers, with 'ярко' (brightly) specifying the visual impression they give.
Цветы в саду выглядят ярко.
The flowers in the garden look bright.
In this instance, 'выглядят' is used to compare the visual similarity in the appearance of the houses.
Дома на этой улице выглядят одинаково.
The houses on this street look the same.
The word 'выглядят' is used to describe the outward appearance or visible impression of the subject, in this case, 'они' (they), with an emphasis on their happy demeanor.