I have over 35 yeas hands on of experience with phone issues such as this one. Also I knwo this particular one well;-)
Not to mention, these Panasonic phones had a few issues back then.
What you will need to do is replace the remote phones that aren't working any longer.
The base should be fine as is almost always the case.
The best place to get new phone handsets is: http://panasonic.factoryoutletstore.com/cat/17594/Panasonic-Extra-Handsets.html?cid=6600&chid=1600
You can call them to order these:
In any case, I will stick with you until this is complete.
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