Omnitron's Interpolation Beam and The Sentinels

Does the 1 damage everytime you draw a card hit all 4 of the sentinels or does the player get to choose?

The wording of the text says "That player's hero"

Choose one of them to take the damage in this case

I think for the Sentinels, anything that affects "A Hero" or "A Hero Target" becomes player's choice on which Sentinel is affected.

Anything that affects multiple targets can affect more than 1 of them.  For instance; "All Hero Targets" would affect all Active members of the Sentinels.  "__ damage to Hero with the highest HP and ___ damage to the Hero with the lowest HP."  If Dr. Medico had the most out of everyone and Writhe had the least HP out of everyone, they would both take damage.

Basically, they are always treated as separate Hero targets, except for certain conditions such as Infection in Plague Rat's deck.  The player chooses which Sentinel is actually Infected, but for the purposes of flipping Plague rat, your entire "Hero Card" is considered Infected (but, only the Sentinel that is actually Infected suffers the affects)

How about Kismet's Jinx that give you -1 damage.  Can I choose to apply that to one Sentinel and then have the source of the damage be a different one?

It would reduce the damage of which Sentinel it was currently attached too.

I agree, I used the same logic to keep Akash'Bhuta's brambles busy in my only game with the Sentinels. Made sure Medico was the lowest so I could keep hitting things with the Idealist. Plus if I needed to use medico, he usually heals so I wasn't losing anything.