Hi, when you ping your ultrasonics you cannot do both at the same time, because you cannot check to see which reflection is from which transmitter.
I suggest you ping one , wait and get a reading, then ping the other, that way you will be sure that you are only receiving the relevant reflection.
Please can you post a copy of your complete sketch, use #code tags, a picture of your project and a CAD or picture in jpg,png, or pdf of your circuit.
You have the project in front of you, we don't, so we need as much information as possible to get up to speed, this way we will be making suggestions that may save you and us time and replies.
Thanks.. Hope to help
Tom..... 