Trimurtis are present in every Brahmanda.

> This Lord, or Isvara, has three aspects: as Brahma He creates, as
> Vishnu He preserves, and as Siva He destroys. These three form as one
> Lord, or God, who is known by three different names according to His
> three functions. **Since the Brahmandas are without number, so too are
> Brahmas, Vishnus, and Sivas without number.** The Purana says: 'One
> maybe able to count the number of sands on the seashore, but one
> cannot count the number of the Brahmandas or the deities controlling
> them.

**The Upanishads, Discussion of Brahman in the Upanishads, The Great Lord (Mahesvara), by Swami Nikhilananda**