So is there a way for two alliances to become one? I was on a path of great unity creating a alliance that would span the galaxy, when my plan fell apart because 3 other empires formed an alliance of their own. I have very high status with them, and am at peace, and even keep getting messages of them suggesting that they might soon send an alliance invite, but there is no option to merge alliances. This is annoying as it would mean that I would need to leave my alliance and joined theirs and then re-invite everyone, which would suck away my resources. 

Also, is there any sort of list of alliance names? I notice they generate different names depending on the factions that found them, such as more sciency ones for sophons and peace loving ones for unfallen

I do not believe alliances can merge but it's unlikely they would be able to in the first place,

As there is a limit to alliance size:

<Alliance>
        <MaxEmpires>Floor($(MajorEmpiresCount) * 0.5)</MaxEmpires>
</Alliance>

By this formula its:

There are 41 Aliance names in the game files:

Accord of Principled Nations
Chorus of Aligned Sentients
Anti-Aggression Pact
Pyrran Aggressive Defense Treaty
Cabal of the Black Nebula
Caucus of Chronus Rising
Möbius Alliance (get it? neverending? infinite?)
Allied Nations Federation
Union of Galactic Empires
The Long Future Community
Project for Endless Development
Society of Sentients
Alliance of Eternal Seekers
The Galactic Fraternity
Sorority of Galactic Leaders
Star Alliance (kidding)
Intergalactic Union for Trade
United Constellations of Sentience
Star Development Agency
Union in Galactic Interest
Society of Like Minds
Intergalactic Cooperative Caucus
Cerberus Treaty Group
Galactic Treaty Organization
The Scorpius Cabal
Future Perfect Research Group
Galaxy’s Edge Alliance
Sorority of Alternate Possibilities
Brotherhood Beyond Infinity
Union of Endless Appetite
Virtual Echo Gathering
Fraternity for Galactic Chastisement
We Are Suns and Dust
Union of the Great Borealis
Pact of the Sisterhood
Memories of the Lost
Constellation of Heroes
Confederacy of Free Beings
Primordial Dust Clan
Bluest Orb Coalition
Colloquium of the Infinite Beyond

I am not sure on what determines which name is picked.

Alright thanks man