Regulated +5V drops when relays are switched on
According to the datasheet, the voltage drop is within spec:

"Load Voltage Regulation 10% to 100% full load ±6% max."
If "full" load is 400mA for a 2W, 5V output version, then you are getting up to 75% load by then. (4.869V / 5.0V ) * 100 gives  us 97.38% of load voltage regulation, which is still within reason. 

I suggest you use a more constant reference.. Some people use a reference (zener) diode or maybe another small linear regulator that goes from 5V to 3.3V but its more of a reference than a 'power supply' so to speak. Basically you need something to act as a stable reference, and not ever-changing due to such large changes in load as one or both relays turn on.

Edit: To use a resistor and zener diode as a voltage reference, see this question and it's answer by Anindo for how to do it, and calculate the required resistance to make it work.
Using a Zener diode as voltage reference