Voltmeter resolution increase by having several in series
simulate this circuit &ndash; Schematic created using CircuitLab
Figure 1. Two digital meters with nominal 10 M input impedance but second one is 10% below nominal.
Since your meters are in series the same current flows through both. The impedances of the meters will differ slightly (although yours are very close) and the voltage read by each will be proportional to their resistances. In my illustration I have assumed that the meters are the 199.9 type which have a full-scale reading of 199.9 mV.

Is it possible to consider the total voltage to be twice 3.626V, so 7.252V? Is there a risk that the voltmeters are interfering each other in their reading, and I cannot use this result?

You would need to understand the inner workings of the meters a bit more. They shouldn't interfere but if the second meter is switching its auto-ranging resistors in and out then it might. If you can turn off auto-range it might help.
Be aware of your meters' capabilities. Look up their specifications to work out the % error (of full scale - not your reading) and how many digits the reading can be out by.