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After being stuck for days and not getting anywhere, I read a walkthrough and i'm supposed to ask Victoria who the person in the picture is in Robert's study, except I can't talk to Victoria as Samuel won't disturb her?

I've done all the tasks in the walkthrough for Robert's study and now can't progress? Is this one of those stupid 'do it in the right order' bugs that you are not made aware of?
Yes, it's one of those 'Do it in the right order' bugs!!

Possible Spoiler:

When you tell Bates about Roberts death, DO NOT click on Victorias door until you have gone into Roberts study and clicked on the picture and completed all the tasks in there. I had an earlier save so went back and completed Roberts study and then clicked on Victorias door, I then had the picture to ask about and not just Ashburry Sanatorium!

So it seems going to Victoria BEFORE you've seen the picture in Roberts study can block your progress in the game!!
Had the same issue. Went to the stables to find Morris' letter and hair sample from his hat had it examined at microscope in the lab then she would talk to me about the picture of the man.