Firstly, well done for realising that you were in the middle of falling for a scam. Changing your online banking details immediately on another device was wise.
After closing this app can the hackers still control my laptop?
Probably not. But it is possible, if they were able to install additional software on your computer while they had access. (Since you could see everything on the screen while this happened it's not likely, but it's not impossible.)
Most scams like this one are not using sophisticated hacking tools and techniques, just good ol' fashioned confidence tricks and scams. Most, but not all. If you are genuinely concerned, back up your personal files and documents and reformat your computer. (Yes, that's the best way to be sure, even if it's inconvenient. You effectively gave a malicious person complete access to your computer as if they were you, even if only briefly.)
Could they see and control what I am doing on other devices...?
No. Even if your home computer is compromised, if your bank has half-decent security practices at all, then the connection between your tablet and your bank should be secure. (Email is a notable exception to this -- anything you send or receive in an actual email can be intercepted by an attacked who could be bothered, but hopefully you didn't use email to change your username and password.)
Other things to worry about: If the scammers asked you any "verification" questions like a bank etc would ("Can you confirm for me the last four digits of your social security number/the number on the back of your credit card/your date of birth?" etc), then you are now at serious risk of identity theft, especially since they now know your bank, bank account details, balances, recent transactions, everything that was visible on your screen.
Either way, you must contact your bank to inform them, and change your security/verification questions to something that cannot be answered from the information they now have, or found out about you online (any information online, you are now extremely easy to find for them). Often identity theft is the real goal of these scams, because it's much more lucrative than just tricking you into giving them money once or twice.
Once again, well done for shutting the scam down partway through. Best of luck.
