I wouldn't have thought that interference between the sensors was much of a problem (the duration of each ping would be very small and you can ensure that only one sensors operates at a time)
It's a very common problem, particularly with inexpensive sensors.
With US sensors, there's a trade-off between high update rate vs. the chance of getting echoes from distant objects.
The simple way of avoiding this is to wait longer between pings, but this reduces the update rate.
You may be lucky to get an aggregate update rate of only ten or fifteen updates per second.
One other way is limiting the sensitivity of the receiver.