Take the hourly IC Direct train, leaving Schiphol Airport every hour at xx:43.

Reservations are not a thing in Benelux (except on Eurostar high-speed trains but you can easily avoid them). Simply hop on and sit wherever you want.

Also be aware that travel in Luxembourg is free of charge in 2nd class. And travel in Belgium is not very expensive.

I tried to purchase my benelux pass thru Eurail website. It charged the full amount and my tickets are not yet issued. Its been 5 days. 

Is it possible to buy this pass at the Amsterdam airport train station at the counter? Would it be the same price?

1. Did you buy a mobile pass or a paper pass?
2. Have you received a confirmation email? If you ordered a mobile pass, the pass number is in that email. With that pass number, you can load the pass in the rail planner app.
3. If you haven't received a confirmation email: Is there any order shown in your Eurail account, in the order overview? If you ordered a mobile pass, then you should also see your pass number there. If you ordered a paper pass, then a tracking code should be visible once it has been sent out.

The international ticket counter at Schiphol airport (and the one at Amsterdam Centraal) should indeed also be able to sell this pass (paper only), for the same price in euros, plus a €7.50 fee. But first check if there's an order in your Eurail account.