It is a common failure of moral analysis (invented by deontologists undoubtedly) that they assume idealized moral situation. Proper consequentialism deals with the real world, not this fantasy.

• #1/#2/#3 - "never knows" fails far too often, so you need to include a very large chance of failure in your analysis.
• #4 - it's pretty safe to make stuff like that up
• #5 - in the past, undoubtedly yes; in the future this will be nearly certain to leak with everyone undergoing routine genetic testing for medical purposes, so no. (future is relevant because situation will last decades)
• #6 - consequentialism assumes probabilistic analysis (% that child is not yours, % chance that husband is making stuff up) - and you weight costs and benefits of different situations proportionally to their likelihood. Here they are in unlikely situation that consequentialism doesn't weight highly. They might be better off with some other value system, but only at cost of being worse off in more likely situations.