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**

> The constituents of creation beginning with mahat (intellect) and
> ending with Visesa [1] (earth) generate the cosmic egg, whence Brahma
> arose like a water-bubble.

**Linga Purana I.3.28**

[1] The group of seven beginning with mahat (intellect) and ending with visesa (bhutas) constitutes the Cosmic Egg which is material, though it derives its potency of consciousness (cetanata) from Purusa.

> He alone is Rudra and Vishnu pervading the universe. These worlds are
> within that cosmic egg and this universe is within it.

**Linga Purana I.3.29**

> The cosmic egg is externally enveloped by water ten times its
> magnitude. The water is externally enveloped by fire ten times its
> mass. The air is externally enveloped by the ether ten times its
> magnitude. The ether is enveloped by ego the cause of sound. The ego
> is enveloped by intellect and intellect is enveloped by Pradhana. They
> say that the coverings of the cosmic egg are seven [2]. There within
> is Brahma seated on the lotus. There are crores and crores of such
> eggs in existence.

**Linga I.3.30-33**

[2] The seven sheaths of the Cosmic Egg consist of intellect (mahat), ego (ahankara), and five subtle elements (tanmatras). (Vayu Purana 4.87, Kurma Purana I.4.46)

> **In all these cosmic eggs there are four-faced Brahmas, Vishnus and
> Rudras.** They are all created by Pradhana after coming into contact
> with Siva.

**Linga Purana I.3.34**