Take some time(now, and in April/May) and get out at night about 11:00 PM and on and start with 1/2 mile grids and listen for those 'yotes to howl. It may take some time and a couple of days on each grid to find them. When they do howl? pinpoint the best you can where the sound came from. If you hear two howl? pinpoint their locations the best you can and wait for another howl or pair of howls. The location where the howls occurs more than once should be your starting point to find the den. We have often sped the process up by using a howler or female invitation on the FOXPRO. We do it to evaluate how many denning yotes are around; then calculate pup counts. Once you have an IDEA where the den is? leg work becomes mandatory looking for den trails(more than one set of yote tracks on a trail; becomes very obvious the closer to the den you get). Following those den trails in the direction they become more obvious SHOULD take you back to the den itself(reference KIRBY description for shpe and size; here, the 'yotes only have one den entrance). Know that the minute you scent up a den site?, mom coyote is going to move her family to another hole and she PROBABLY has a dozen or more to chose from.
Good luck. To much more to add here that would help even more.
