From the pictures it almost looks as if there's an ESP8266 in there, but next to the STM32L152D does not make sense I guess
Bluetooth module
Yes, that's right, it looks like it's on its own little soldered-on daughter board, as I've seen before with "jellybean" bluetooth modules.
As for the DMM IC, my guess for the DMM front end IC is maybe the
Hycon HY3131 or the
Fortune FS9704B? The UEI DM397 DMM uses the 50,000 count FS9704B IC, but I thought the 50,000 count HY3131 seemed like a better feature match (eg, runs at 3.6V). But it might be neither of those two, maybe there are other dedicated 50000 count DMM IC chips out there?
And the DMM IC would work in conjunction with the STM32L micro I presume. I don't know too much about that area, but I'm interested in learning a bit.