Someone may be able to correct me on this, but are not 26inch road wheels actually 650c road wheels?
You are right. 650C is one of the sizes known as 26". Also 650B which is the one that's common on small size road bikes. I wouldn't want to stick my neck out and say that this is the size the OP needs though as the description of the bike is so vague (and there is still that mention of 700C, even if it's misquoted as the frame size)
The suggestion of looking for the size on the rim is excellent of course
. (Kicking myself now for not having said it
) The options are that it could be stamped into the rim, on a sticker on the rim or under the rim tape somewhere (as already suggested).
The size might be in the ETRTO format which will be 3 number rim diameter x 2 number rim width (EG: 622x17)