You could definitely point a bunch of microwave equipment at someone's room and cause some damage, that's not in question - but to somehow cause a bunch of neurological problems, but not leave thermal burns, or heat up jewellery, or fry electronics?

And this isn't a "with todays tech" issue either. This is all being proposed as being totally possible with 90s-era technology. The sheer amount of wireless tech innovation and availability since then has been enormous - what feels possible today is ignoring that in the 90s a cellphone looked like a brick with an antenna on it. Solid-state microwave elements weren't COTS parts you bought from China in bulk.

We're talking about doing a lot of very difficult to do things, with equipment and power outputs which would require substantial draw from either residential electricity supply systems, or banks of lead-acid batteries (no lithium ion in that age either - so you have a transport and weight problem).

The more disperse you propose the signal is, the less plausible it gets too - at some point your number of field teams and the size of the equipment is going up and up and up and all of this is happening within line-of-sight (or near enough) of a target - microwaves don't penetrate multiple buildings.