Well. Quite a lot of information then. And I suspect some disinformation.
First, both the index listings I copied from the GRONI web site have the identical date (21 July 1848), place (Coleraine) and reference number (M/1848/K1/1070/1/98). So this is clearly a marriage of a Samuel Hen(d)rie/y to a Mary Campbell. As is the one on 27 October 1848. I find it rather stretches my credulity that two Samuel Henrys should have married two Mary Campbells in Coleraine within just about three months of one another, but it's not impossible. You need to get the image of the other certificate and compare what they say. If both sets of residence and fathers' names are the same, I would incline to the view that these are two records of the same marriage, but if there is a difference, then they must presumably be two different couples.
I am not too bothered about the variations in the dates quoted in the children's birth certificates, because it's quite common for people to get this wrong, especially if they could not read and write and therefore could not check that what was written down was correct. Also, it is not unheard of for people's death certificates to have incorrect information, because obviously the person registering the death could only supply the information they knew, or thought they knew. It even happens that wrong infomation gets on to marriage certificates, especially if the people involved could not read or write.
So although the information is conflicting, I think that it is still possible that it is the same couple, and that more evidence is needed to be sure one way or the other.
Is t worth viewing the 21 July 1848 m/c? Or is that the same couple entered twice for some reason?
I think it is essential to view it and see what it says. Whether it is worth it is something you will only know after you have got it.