Your pictures didn't upload.

Ugh.  Will try again.

Can you see the picture now?

It is hard to read.

What does the designer of the house have to say on the issue?

Has construction of the house started?

We haven't talked to the architect, just the project manager and air/heat guys.  To add more stress, they want a decision immediately and my husband is a tax accountant.  Timing couldn't be worse.

Not enough information. Size of house, how many levels, how many units, zoned hvac, any attic or basement space, etc?

Construction is underway.  I am just sick.  My husband kept asking if we needed 2 units during the design phase and was told we did not.  We could have designed things differently.  Now everything is framed and our options are all not great.

Utilize the space under the porch for either duct space or a mechanical room. Talk to your architect as soon as possible.

Some things don't make sense, even at this tiny scale that is unreadable. It looks like you have stairs going to a basement. Why is one unit on the 1st floor then - how is air ducted to spaces on the 1st floor? The 2nd unit I assume is for a sizable 2nd floor. Does placing that unit on the 1st floor allow ductwork to mess up ceilings on the 1st floor? There are options, depending on other factors, to put a unit in the attic, or just put ductwork in the attic, have the unit on the first floor with only a trunk up to attic, in the basement with a trunk up to attic, on the 2nd with trunk to attic . . . . a few possible ways but it should be designed in tandem with the 1st unit, the house design, the CFM to each room, where returns are, where the condensers are, where intake is, how much room you have to house a unit, . . . . yes basically designing from scratch as it should have been. Even if you have rough framing done, design it right as if you hadn't broken ground, then change the framing to meet a properly designed system - even with extra cost and time wasted you will be much farther ahead long-term rather than just throwing in another 2nd unit to what's quick and easy.

I would get a few opinions if you can - we ended up needing a 2nd unit and a talented/creative HVAC expert made it work in our attic, he changed the original zones and its works much better this way. Don't let them push you too fast on a very important decision -

Editting to try better pics. The one I posted before is our lower level where they were planning to put both units. I am checking to see if the attic is an option. The proposal is to have each unit cover one side of the house, not main floor and lower level. They are doing that because the main room has high vaulted ceilings.

Let's try these pics... lower level with unit location options

Main level plan

You have this large room labeled "mechanical/storage" already. Why can't it go there?

What direction do those windows face? Is the limiting issue - a/c or heat?

I think generally you got some bad advice and planning. I think these issues are very difficult for internet advice. You need another HVAC opinion.

Your project manager (in my world, it would really be the owner of the company not the PM) needs a sit down and talking to on April 19th. This is not something to be rushed. Planning takes a lot of calculations and load and duct calculations should be done a long time before crews are ready to work. Especially on a large and HVAC challenging house.

Upgrade the exterior house shell, attic insulation before installing another unit. Personally I want my bedrooms to be the same temp, never cared about the living room a little colder.

If one area just add Mr Slim.

After posting and AC vs heat pump question here myself it became glaringly obvious that getting all the needed info across online was impossible. While general advice was possible the detailed nuanced info that was specific for our house needed to happen by soMeone coming in person and helping us.