Yup. Eliska=Elisabeth.
So Albrecht it is. What do you make of the mini war over the Habsburg inheritance? Averted, delayed or goes ahead as OTL (just with a different casus belli perhaps)
I don't think any of the lines will allow Wilhelm's son to succeed. First we'll have a regency like you said and they'll attempt to buy Wilhelm out because it'll be just too difficult to rule Naples and Inner Austria at the same time. Probably best if it goes to Ernest the Iron still. Ernest could pressure Joana to relinquish inner Austria on behalf of her son, probably with some monetary compensation.
Joana & Wilhem's son should be raised in Naples if he wants to rule there. A family compact with the Albertine and other branches of the Leopoldine line could also serve as a guarantee for her. Usurpers, the papacy and the nobility might be less likely to mess around now that there is
A. An heir
B. Well connected heir with family that'll probably press for guardianship over her son if any funny business (assassination) happens to Joana.