I just connected two 18B20 sensors to my Wemos D1. Works perfect, just one big problem is that the temperature difference from these two sensors is around 3.81 degrees at room temperature (both in 12 bit resolution). The sensors are on a breadboard, sitting next to each other.
If I understand the documentation correctly, the accuracy of the 18B20 is +- .5 Celsius, so the difference should be +- 1.0 Celsius?
"A man with a clock will always know what the time is it. A man with two clocks will never be sure"
(Alberto Puente. Engineer. La Felguera 1952 - Madrid 2014).
Accuracy, precision and resolution are not, by no means, synonymous; have a look on this link.
Those sensors have a "sentient" element (usually a temperature sensitive resistor) plus some electronics that convert this electrical magnitude into voltage and, in this case, (converts) the latter into a series of bits. Being the two last processes digital, we can't expect that they deceive us (even if, as is it the case, one uses one of those awful breadboards).
Although 3 ºC are too much, may be that one (or both) of the sensors are (quite) wrong: you can't ask for much accuracy from so cheap sensors.