Thank you again for your replies! I actually paid for their seats already as it seemed like a small amount for peace of mind. I will enter their passport info today, I luckily have everything and then they can find a library - (brilliant idea!) or an internet cafe.
I do have them booked at the Premier Inn in Paisley at the retail park(thank you!). The problem is that they arrive around 2pm on the 18th and want to tour Glasgow. Their flight departs 3pm on the 19th. They have a BritRail pass with is good through the 18th only. So all transportation on the 19th would be extra. They really want to be in Glasgow for ease of sight-seeing and then go from there to the airport.
I have researched both the University housing options and airbnb and both do seem like they would work. I forwarded this to my daughter, but alas as she does not have internet access right now, I am unsure of when she will logon again. I sent her a text too. :-)
I am the one who suggested it would be difficult catching the plane on the 18th as they wouldn't arrive into Glasgow until 2pm if all of their connections went as planned. If anything was late or they missed a connection, then they wouldn't get to the airport on time. So I suggested touring Glasgow for a day. Seemed like a great idea at the time. Who would guess that was the one day all of the hotels would be booked.
Thank you again - you have all been so very helpful. Cheryl