Buying Tickets and Express Pass the day before

We are staying at Cabana Bay for 3 nights in August. I am planning on arriving and relaxing at Cabana Bay the first night and then hitting the parks for the next two days. Can we buy tickets and express passes on the day we arrive at the hotel or at the gate for the following two days? We are coming from the UK and it seems impossible to buy the Express Unlimited Passes in advance from this side of the Atlantic. Thank you to anyone who can help! try these link for universal.
Undercover tourist are popular .
Buying your tickets from a third party might be cheaper but you will need to factor in exchange rate costs and shipping costs if any. You will not need unlimited express standard exp pass will be enough as with only 2 days you won’t have a lot of time for rerides.
To answer your question yes you can. You can also buy express pass in the park on the day after buying your tickets from elsewhere.

Great - Thank you very much. I will check out these links. I thought of getting the express passes for one day to hit lots of rides and then see the parades, shows and less popular rides the second day. My kids are younger so the thrill rides are out which means there are less rides to go on but we might go on them multiple times. Maybe we will wait until we are in the park to decide if it is worth it. Thanks again!

Waiting to buy exp pass is a good idea. planning on 1 day park to park exp pass and one day w/o it is also good. I would attempt to see what you can do w/o it on your first day If you can make early entry for wwohp which might be 7 am in Aug then you can get so much done before 11am. You will be an hour in front of all the offsite visitors with tp and it make a difference. Single rider queues are really good as is child swap depending on the ages of your kids. You all enter queue together and let the first TM know you want to use child swap. Close to loading bay there are air conditioned waiting rooms with water fountains etc. One person rides then you just go to the room and swap looking after the non riders. You should be able to use child swap with exp pass as along as all of your party that meet the height requirement to enter the queue have exp pass.

Air conditioned rooms with water fountains sounds good!
Thank you