No.
Yes, Yes. You can split the transformer output but it’s important to insure you maintain polarity. The best way to do that is to buy a CCTV power splitter
Up to a 12kW system should be able to simply clamp a 50A CT to one of the inverter output lines.
Two units presents a challenge in aggregating the data. If the solar is monitored by the same unit as the mains, you can get the solar picture and/or upload to PVoutput. To get a complete picture, of the whole house, you need to setup the IoTaWatt to upload data to an external server. IoTaWatt supports influDB and Emoncms for that. More technical users seem to prefer influxDB, and others like Emoncms.
Here is a post from a recent similar install uploading to influxDB.
I would advise first looking closely at what you want to monitor. IoTaWatt has 14 inputs. Two go to the mains, one to the solar, and then you have 11 remaining. Most homes don’t have 11 big loads. I realize that there are a lot of circuits in a US panel, but most of them typically don’t represent any real consumption. There are also ways to aggregate multiple circuits into a single CT and multiple CTs into a single IoTaWatt input. For example, in my kitchen I have two plug circuits, microwave and range-hood. I run all of those conductors through one CT and call it “kitchen”. I have an 8 circuit subpanel that feeds bedroom and bathroom plugs - I have a single CT on that. At the end of the day, they don’t amount to significant usage and I can still see the signatures of individual appliances. That’s 12 circuits covered by two inputs.
So my recommendation is to get one IoTaWatt and see what it tells you. You can get extra CTs and combine them, and if it comes to that, you can always add another IoTaWatt. Keeping everything to one IoTaWatt in a residential setting is much simpler.