"Low FID threshold" refers to the company's ability to make a FID on a vessel without having to sellout the full 3.5 MTPA that the vessels can produce. According to the company, they only need to contract 2.0-2.5 MTPA to make FID on each vessel.
It’s simply saying thresholds (plural) because there are multiple ships and each has minimums to meet FID. Looking way too deep here. You can FID the ships separately or as one group, but each has it’s own threshold, hence the plurality