First of all, I’m afraid you won’t get good interferometric results over vegetation with C-band.
The risk of misalignment is given, so using one master would be the better choice (AB, AC, AD, AE,…). As far as I understood it, getting interferograms between slave images is not yet possible in SNAP. Maybe this topic helps you:
You could first create different interferograms (AB, BC, CD,…) and then co-register as explained by lveci.