buy a small mixer or interface with a usb output then you can input the output from the mic and the electric guitar directly into the pc. I am assuming that the backing track from BIAB is playing through the pc?

i have this
https://smile.amazon.co.uk/Behringer-U-P...C146&sr=8-4

and it will take the guitar and the vocals and record to BIAB whilst the backing track is playing. mind you balancing the guitar against the voice might be trial and error.

i think in RealBand you can record the guitar and vocal on separate tracks so that would be better.

start the camcorder to record your performance. I am also assuming that the BIAB backing track is playing through speakers so you can hear it - headphones will spoil the look of the performance! you won't get too much problem with sound bleed from the backing onto the live recording of the vocals (the guitar won't be affected).

you will now have a video on the cam corder and a soundtrack on the pc. mix the soundtrack to a single wav file. assuming you have a very basic video editor you can then marry the two together. you might need to clap before the performance ( that's why movies have a clapper board) so you can synchronise the sound and the video - when you see the clap the noise should be at the same time. then edit it off to leave just the performance. if the backing track does bleed onto the vocal if you synch things properly it shouldn't matter.

here's a link to a free video editor but you'll have to look hard for the link to the feee version for home use

https://www.nchsoftware.com/videopad/index.html?kw=free%20video%20editor&gclid=Cj0KCQjw0IDtBRC6ARIsAIA5gWuYmImp0S1cfu5JRKQOlqeSszrePk1vsj4frxRX82FGbwZPZMUN138aAl55EALw_wcB

good luck