There is always name of female before male like Siya Ram, Radheshyam then we say Shiv Parvati not Parvati Shiv.
I don't think that there are any such strict rules. As a proof, see the verse given below.
LakshminArAyanau vAnidhAtArau girijAshivau |
Srigurum gurupatnincha pitarAviti chintayet ||
Guru and Guru's consort (Gurupatni) should be thought of as one's own parents. They are to be thought of as Lakshmi-NArAyana, VAni-BrahmA, GirijA-Shiva.
KulArnava Tantram 12.35.
Note that here GirijA is a name of Goddess PArvati. So, seemingly there is no such rule like we should only say Shiva-PArvati and not PArvati-Shiva.
The Sanskrit has two basic rules of thumb:
First, a sentence is not made up of words, but of phrases. The beauty of this language is that these phrases can be put in any order but the purport of the sentence never changes. For example, let us look into sentences given below:
(i) vrichhat patranni patanti, (ii) patranni patanti vrichhat, (iii) patanti vrichhat patranni, (iv) vrichhat patanti patranni, (v) patanti patrani vrichhat, (vi) patranni vrichhat patanti. etc.
All these sentences above in the example have the same purport and the meaning therein.
Second, "Visheshan" and "Visheshya" when mentioned in a sanskrit phrase, the "Visheshan" is used as prefix to the "Visheshya" or as a salutation in a general practice. Radha, Laxmi, Sita (siya) are "Visheshan" of Krishna, Narayana, Rama as the "Visheshya", respectively.
N.B. The Sanskrit "Visheshan" and "Visheshya" are somewhat equivalent to adjective (quality) and noun (name) respectively, in the English grammar. The consort and the wife has some difference in the Sanskrit usages. The consorts are typically used as the "visheshan" or adjectives in Sanskrit phrases.
The rule of thumb and its origin, however, has some humorous references:
Shiva parvati are most beautiful eternal couples in all decades with complete family force Shivena parvati Shiva also parvati without parvati there is no shiva If u say only shiva, goddess parvati present in his body entire half or may full body If u say goddess parvati lord shiva present in her complete form Shiva parvati are not different they are one their couple bonding such a way that they cant leave without each other Without parvati their is no shiva nothing