So someone outside wants radio and you want tv inside. Sounds like something that happens to DW and I a lot.
I don't have the issue you do, but it seems like the back of the outside speakers aren't enclosed. Basically the rear part of the speakers might be venting sound inside due to them not being closed in.
You might try to validate by removing a speaker or if you have access to look at the rear of the speaker through a panel or cabinet.
If this is the case a product similar to
THIS might help some. It would be best to enclose the speaker in MDF, but doubt you have access for that.
Remove speaker, put in foam, cut foam to fit, and remount. Be sure to seal for leaks.