We used to breed dogs, so here goes.....
Bitches come into season usually every six or nine months and can bleed for anything up to about 3 weeks. They can start to come into their first season at 9 months of age, but it's more likely that she wont have her first season until at least 12 month and certainly should not be mated until at least 18 months of age.
The height of their season is when mating takes place and this varies from bitch to bitch. Mine have varied from day 9 to day 19 of their season.
When a bitch is in season, she will only be interested in the dog when she is at her height, he however will be very interested in her throughout it all !!
Having him neutered is a very severe solution IMHO, especially when your brother can go to the vets and get some pills that will stop his bitch from coming into season whilst you are staying with them.
Should your dog cover his bitch and she falls into whelp, well there is only one solution that I can see......CHARGE HIM for the privilege !!
PM me if you are really worried.
Ripha.