They attenuate maybe the standing waves that maybe create ?Also and my signal right?
A mixer (especially a diode ring mixer) must "see" the 50ohm impedance on all its ports, otherwise it will leak..
Pi or T attenuators may do it as they "match" to 50ohm (while they do attenuate a little bit..). You may match with other matching networks as well.. The resistive attenuators are easy to design and they are broadband, with L/C matching networks you have to match at specific frequency of interest.
On that ring mixer you cannot expect to see clean sine wave on any port as the isolation is not too big, and, the signals will be full of sums and differences of the LO and RF signals (plus sums and differences of all combinations of their harmonics).
Your crystal filter must be matched (50ohm input) to the mixer's 50ohms output, and when well designed you may see on its output a "clean" signal (which fits in its bandwidth)..