You can expect "cross-talk" when operating 2+ transducers on an identical frequency. This "cross-talk" is created by the intersection of sonar waves (cone angle when referring to high speed transdcuers) as they intersect one another somewhere below the boat. Most users who require multiple transducers of the same frequency will simply turn one off. The only way to determine an outcome with 2 transducers of the same frequency is to: #1 - completely wire your electronics and install the transducer you know you will use and #2 - wire your 2nd set of electronics and while both units are on, drop the transducer over the transom, or, better yet, temporarily secure the 2nd transducer in various proximities to the 1st.
Safe boating....
Captain Chris