if i was in andres position(which i wouldnt be way to much drama) i wouldnt want santi near my family either tbh he lost the right to be the mc's father when he abondoned him. If im the mc id rather think andres was my father than some deadbeat who left did he go about it the right way probably not but i think he did what he did with good intentions
Technically yes, however, not to deep this but the best thing a stepfather can do for his stepchildren is to have the actual father involved in the rearing of the child. Children in general, but especially young boys need their biological father in their life to have a sense of identity. It's been awhile since I've gone through the research on this but while your position is understandable and potentially even noble, it might not actually be what is best for the child.
There is of course the case oh what if the child doesn't know the stepfather isn't the real father, I believe in this case the above still holds. There might bet a possibility that it doesn't matter in the situation in which both stepfather and son don't realise they're not related however I think this is still not the case and is certainly not the case in this situation. There is an asymmetry in the relationship between MC and Andres. Andres doesn't allow Emily to tell MC. Andres should have discussed with Emily what his concerns might be and they should have came to a decision together. I don't think they're makign Andres out to be that much iof an asshole, just that he is at the very least now a dick and MC's newfound forgiveness for Emily makes it appear as if we ought to hate Andres when really it just MC realising that he wasn't with his dad because his mum didn't want him.