Hi,
Looking at a map of parishes in Suffolk, Snape is some distance from Bawdsey so I just wonder if you have the right family.
Having said that, I can't find another couple that fit the times. Of course they could have moved for work purposes and there are some couples having children in Boyton with Capel St.Andrew. which would be mid-way between Snape & Bawdsey. I think there are at least a couple of "Markham" families as the dates of baptisms overlap those in Bawdsey & Boyton.
Not much help I'm afraid.
Alan