Lounge access depends on what kind of business class ticket you buy. The FRECCIALounges page says
Who can enter
You can enter with [...] an Executive or Salottino ticket or a carnet of 10 Business travel tickets.
Clearly saying a single business class ticket is not enough but the more expensive ones are.
BTW the same is true for the FRECCIAClub ...
The Freccebianca experience is summed up really well by Show Me The Journey:
There are lounges, including, as you asked, at Roma Termini
If you are travelling in 1st class, there will be a trolley service of complimentary snacks and drinks – prosecco is one of the options, espresso as well
As food is on a trolley only, no kiosk/restaurant (although travel ...
Generally you should get seats next to each other if you reserve in a single booking.
You could also try your luck making two individual bookings in rapid succession both requesting window seats. Normally seats are booked from one end of the train to the other so that might get you something like a 50% chance that you land in adjacent facing seats.
Most of ...
If you book early you should get "perfect" seat in the sense that you will sit next to eachother. If you want to sit in front of eachother then it's probably a bit harder and you then have two ways of accomplishing this:
You can try asking customer service (maybe a boutique at the station) if they can assign you specific seats. Some of the agent are more ...