How old is the house and what is the actual SEER rating on the A/C’s. I had an almost identical situation recently. I replaced an older 200A service with the same and added two 100A sub panels. One was side by side of the main and the other was installed near the guest house that was just built. The pool company also added another 70A Subpanel after the fact near their equipment. Haven’t seen or heard of any problems with flicker at this job or others like it. You do have to make sure that you have proper voltage from the utility under load (both before and after you do the work) and the actual loads need to remain below the main breakers rating. Yes the panel loads sound excessive but most of it is redundant and mainly for show.
Most small residential sub panels are rated for max 125A but you can always use a smaller breaker to lower the costs when 125A isn't really needed.
