While we know the Homeworld was blockaded (at least at times), we also know that it's possible for Yeerks to get in and out of the blockade. Edriss has no trouble with it in Visser, for example, or at any other time. Maybe the Andalite blockade had to be lifted at some point during the war and was reestablished some time afterwards. In any case, it is pretty clear that yeerks can infiltrate and exfiltrate their homeworld, as well as send and receive messages.
Huh? When in Visser did Edriss ever go to the yeerk homeworld? Doing a quick Ctrl-F through the e-book, the only time the yeerk homeworld is ever mentioned is when she says that she named her daughter after one of its moons.
I'm pretty sure that the yeerks never communicate with, much less go to, their homeworld after the first ones leave. The Council of Thirteen is scattered throughout space, and the Hork-Bajir and Taxxon worlds are their biggest strongholds. So, even if they could get through the blockade, there wouldn't be much of a reason to. This is pretty consistent throughout the series, and anything that indicates otherwise is probably a KASU.
And yes, the Andalites probably don't have much of a presence on the surface of the yeerk homeworld. However, the yeerks there are still cut off from the rest of the universe, including the empire started by their brothers. On an interplanetary scale, the planet is effectively under Andalite control.