Honestly? Most experienced (read for that, often asked a lot) critters will only read a whole novel by someone who they a. Know writes a certain standard and b. Takes critism. Without any prior relationship, I'd never offer ( and I'm pretty good at taking on crits.)
Your brother's best bet is probably critters.org BUT they only do SFF and their RFD ( requests for dedicated readers thread) will show a sample, after which they'll decide whether to offer. Also, turning up as a newby without a history of critting makes it much less likely to get an offer.
Also, if I critted his novel, I'd expect him to crit - in line edit detail, as that's the sort of crits I do -- mine. (Well, I might not, cos I'm between books, but you get the gist.) is he prepared to set the next three months aside to beta read for others?
To read and crit a full novel takes days/weeks and, whilst your brother says he has edited, to be very gentle about it, I thought I'd edited my first novel when I got here, and it needed another 18 edits/rewrites to get to the standard needed.
Has your brother considered a professional editing service - Teresa Egerton and J.S.Maryatt from this site offer them. They cost a bit, but it may be a route forward.