Eurorail then eurostar reservations?

The seat reservations are $35 to $45 on Eurostar with a Eurail pass. You should book that as soon as you have the Eurail Pass as it is possible you won't get seats together or at all depending how close the date you are traveling. The summer is the worse.

When is this trip? If you are only seeing very expensive Eurostar fares it is possible that the passholder quota will be exhausted too already.

What you can do is go to www.raileurope.com.
On that site you can do passholder reservations, without needing to have the pass already. So do a search for London - Paris, for your travel date. Add the passengers, and add the Eurail Global Pass under "railpass".

When the results come up you will either see "reservation required", with the price of the reservation, or "rail pass does not apply to this trip", showing that passholder reservations are already exhausted for that train.

I am booking for a month from now. Am i going to get stuck with buying euro rail passes for six and then not being able to able to buy eurostar tickets and then end up having to pay even more. (So about 3800$). Ugh.
Ok and i get people are like you should of made reservations already but my job is a seasonal business and i dont like to book things that i am not even sure that i could afford before I actually know.

I rarely book train ticket more than a week out... :-)

But anyway: You can use Rail Europe as I suggested to find out if there are still passholder fares available before you buy the pass.

Believe it or not it is about 70 %cheaper to fly London to Paris next month. Eurostar is a railroad monopoly.

Yeah we are flying to londom but its from london on i need for thr train :0)