His house and my house is close to school canteen (I used "is" instead of 'are" because we are co-owner/sharing one house)
His house and my house is close to school canteen (we both have two different houses but i still used "is" instead of "are" because we each have one house)
I know his mother and your mother are sisters( here i used "are" instead of is" because we talked about two mothers)
Confusing and wrong. If you are sharing a house say "Our house is...". As there is one house it is confusing to refer to it as two things. Although this is sometimes done as trick (see below).
No. Two houses so use "are". Better might be "Both our houses are ..."
Correct, two women
The trick question
Elizabeth, Lizzy, Betsy, and Bess,
They all went together to seek a bird's nest;
They found a bird's nest with five eggs in,
They all took one, and left four in.
If you are not playing such tricks, don't say "His house and my house".