My boy just got into CDNIS reception, and it was a struggle of choice between IMS & CDNIS. (he also has ICS & ESF as options but we prefer the first two listed above).
Personally I believe in the Montessori system so my son was in DMS (Discovery Montessori School) from age 1 until now (that he's moving into CDNIS). Bilingual is not our prime requirement but DMS & IMS are both bilingual KG with pre-nursery/ Playgroup.
Given your prime target is bilingual IS, would you consider other bilingual PN such as Victoria & Kingston? If RMK is one of your choice, then I think you may not like Montessori (they are two ends of the spectrum), but do take a look at the education philosophy behind it, which IMHO is very beneficial for a child in the long run.