2 voltage measurements same circuit Arduino Uno
All arduino ground pins are connected together. If you connect a ground pin to each side of the 5ohm resistor, then it short-circuits the resistor. 

Put everything on the same schematic, and just have one node labelled ground. It's much easier to see what's going on if we put ground at the bottom, and put components vertically, following their voltage (when we can). For instance like this ...







simulate this circuit &ndash; Schematic created using CircuitLab

The voltage across each component can be computed as the differences of voltage you measure at each node. So your battery voltage and R2 voltage are measured directly, the R1 voltage and ammeter voltage drop have to be computed. 

Note how giving the components numbers, aka reference designators, makes it easy to talk about specific components, another tip for drawing of schematics. 'The 5ohm resistor' works for circuits of this size, but runs out of steam if you have two 5 ohm resistors, or values change.