I used to measure temperature on the Raspberry under different load.
I remember if you used something on the USB port, or the ethernet, the chip driving USB and ethernet becomes hotter than the CPU.
(I have a 3B+) But this should be true on the 2B. Anyways, the differences will be very very tiny.
Try find an infrared thermometer if you want to be sure ...
The SHT25 has an I2C interface. Use this I2C interface to connect the sensors to the Raspberry Pi. There are many online examples, and sample code; here's two that look reasonable:
Raspberry Pi I2C - Python
EDIT - 20190703:
As Dmitry has pointed out in the comment, you will need to overcome a limitation that's "built in" to the SHT25 ...
I'd like to offer another way, from the datasheet it seems that your ICM-20948 also allow SPI, so you should go for SPI, and not I2C.
With SPI you'll be able to use any number of device, however you'll need a pin a per device to select the one you're talking to.
I think this will be the best solution for you. If you're using Linux, you'd be able to add ...
This is due to the fact that you are computing RMS (Root Mean Square). There is nothing you can do against that and it will always be (unless you opt for a different type of circuit).
To have the resulting RMS equal to zero means the signal coming from the CT is a perfect straight line. However there is always a tiny current change on the divider that you ...