If he is related by blood to the founder, it is a sur name. otherwize it is a lastname.I've always seen Neverar before Indoril, same wit Lord Helseth Hlaalu
Either way works with those names, both are used frequently. Indoril Nerevar, Nerevar Indoril, it just depends on who you are talking to.
A bit off-topicish, but who exactly founded House Indoril? Was it Nerevar or St.Olms? And were they both related?
Nerevar founded it, with some help from Almalexia. Turns out Almalexia has more sway over Indoril than Vehk, she's actually the one that gave the Ordinators to Vivec for his own city. He does have control over the Ordinators in Vivec city, but this group of elite guards are just a small portion of the Great House Indoril, most killed themselves after the Armstice, and the rest are pretty much integrated into the Temple.
So to answer your question, Nerevar and Almalexia founded it, but Olms was probably the head of the Ordinators in Vivec. They were a house before they were Ordinators.