We have 2 water meters on our property; one for the main house and another for the guest house. We sometimes experience a drop in pressure if we use both showers plus any other fixtures at the same time in the main house. We only use the guest house periodically (when we have visitors) and there's only a .75 bath and a kitchen sink so it always has very strong water pressure. QUESTION: Can we T into the 1/2 line in the guest house and run a line over and T in to the the main house to boost pressure? Would we see any meaningful change by doing so? The expense would be mostly in the cost of the 8 or so ft of copper plus fittings. Thanks a bunch for your response.
Your pressure drop issue is really a problem with flow capacity. You will not be changing or improving the flow capacity of your main house's plumbing system by tying in that 1/2" line from the guest house and will likely see zero improvement by doing so.
You would be better off trying other things: Install low-flow water saving shower heads (this will help more than you think).
Check your water meter outlet size and ask your service provider to install a larger one if possible, then replace the main service line with larger pipe (I know, big job).
If you have a pressure regulator anywhere in the system, check it for proper operation. Raise the pressure setting if possible (check with city bldg. dept. for max allowed).