No Neutral in the light switch is the standard way in most homes in the UK.
Neutral goes direct to the light fitting while the wall switch(es) interrupt the Line supply. There is also usually a constant live Line (unstitched) available at the light switch.
The best solution is usually to locate the microprocessor near the light switch and sense a change of state in the power coming from the light switches. You then process the change of state of the switch to mean that you toggle the light. If the light is already on then you turn it off - regardless of whether flipping the switch from one position to the other has actually turned the Line supply on or off. All you're interested in is that it's changed, so you flip the state of the light.
How you go about interfacing the mains voltage supply from the switch to the Arduino so that you know the power state has changes isn't something that I'm going to get into.
Current sensing the supply from the switches using no-contact induction sensors wont work, as the power from the light switches isn't actually going to the lights - if it did then you wouldn't be able to control the state if the light with the microprocessor.
If you do find a way of safely detecting the state of the supply from the switches then the approach I've just described will only work if there is an un-switched Line supply available at the light fitting, as this is what you'll be feeding the lightbulb with via your relay, once you sense what the light switch (and the Blynk app) is telling you to do in terms of switching the light on or off.