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Do some more number crunching on the coil outputs and required temperature does the boiler output match the fan coil required output?

Even if not in condensing mode all the time, the condensing boiler can run safely with lower temperature than that hair pin boiler

But the bigger win is the modulation, Id look at two boilers, maybe two 180k that would give you a 20-1 turndown 
Plus the redundancy of having two boilers

It’s 100% possible to condense with fan coils. You might use a larger delta T than you typically do, or may consider slowing the fan speed or switch to fan coils specially designed for lower temps. Or some combination. 

Standard practice in fan coil design when that building was constructed was to use a supply water temperature of 180° F. and a return temperature of 160° F. Typically with fancoils this cannot be reduced very much even on mild days, because occupants are likely to complain of cold drafts.

Although high-efficiency boilers will work, they will not condense much if at all, so they will operate more in the range of 85% efficiency than the 90+ percent advertised. They also have a shorter lifespan than a conventional 80% efficient boiler, need more frequent maintenance and generally use expensive proprietary parts.

Bottom line: standard efficiency boilers will almost certainly have lower lifecycle costs. They will also last longer and be easier to maintain and repair. You can still use several boilers to make up the necessary capacity. They have to be piped carefully, primary/secondary is probably the best way.

It's really the typical and very basic questions. How much power must the fan coils put out? And what temperature do they need to run at to achieve that power output? The first question involves doing a heat loss calculation on the space each fan coil serves, and then finding the specifications for that coil (some of the guys here can probably help) to determine what water temperature is needed.

Once you have the water temperature and to9tal power output you need, you can select the boilers. The temperature is the key question on whether you can go to high efficiency boilers, which only achieve those efficiencies at lower return water temperatures.