Ad free app to run dual apps for old android phone

Yes the built-in Work Profile is the best in terms of minimal resource usage. @ OP A Play Store installation is created in the Work Profile for installing apps. I keep the Store app disabled most of the time and only enable it when required which significantly reduces RAM usage. Island app provides the necessary options. However a very few apps like Payzapp will refuse to work (it actually logs out the user!) if Play Store is disabled. For them it has to enabled. 

For unrooted devices the Github version of Island allows the installation of apps outside the Play Store. Rooted devices can make use of Swift Backup etc. 

P.S. A few like Bajaj FinServ refuse to work in Work Profile. Magicpin installs fine but blocks coupon usage. 

Edit: No ads in Island.

Even the 8+ years old SD650 can handle dual apps well enough albeit running highly optimised custom ROM . The main constraint is RAM. In A11, 3GB is borderline sufficient in this regard. 

After the latest Pockets app update made it practically impossible to use it in the Mainland in case of Magisk SU rooted devices I have had to use one of my  accounts in my 2GB Redmi 3s (Kernel SU rooted so Pockets can't detect root as long as the KSU app is uninstalled before the latter is installed) and as expected it's a tedious job. A12+ is significantly more memory hungry.