If you are level 1-4 then it works as you'd expect. After you reach level 5 though you aren't allowed to use Twinned Spell on Eldritch Blast. The parts I highlighted in red is the main reason.
When you cast a spell that targets only one creature and doesn’t have a range of self, you can spend a number of sorcery points equal to the spell’s level to target a second creature in range with the same spell (1 sorcery point if the spell is a cantrip).
To be eligible, a spell must be incapable of targeting more than one creature at the spell’s current level. For example, magic missile and scorching ray aren’t eligible, but ray of frost and chromatic orb are.
is incapable of targeting more than one creature at the spell’s current level
If you know this rule yet are still unsure whether a particular spell qualifies for Twinned Spell, consult with your DM, who has the final say. If the two of you are curious about our design intent, here is the list of things that disqualify a spell for us:
The spell has a range of self.
The spell can target an object.
The spell allows you to choose more than one creature to be affected by it, particularly at the level you’re casting the spell. Some spells increase their number of potential targets when you cast them at a higher level.
The spell can force more than one creature to make a saving throw before the spell’s duration expires.
The spell lets you make a roll of any kind that can affect more than one creature before the spell’s duration expires
what happens if you do a warlock-sorcerer multiclass and cast eldritch blast?
If you are level 1-4 then it works as you'd expect.
After you reach level 5 though you aren't allowed to use Twinned Spell on Eldritch Blast. The parts I highlighted in red is the main reason.
Meta Magic rules:
Sage Advice Compendium:
But you can still quicken Eldritch blast, and cast it with your action and bonus action.