who has more chances of getting approved for a house loan?

Both would be equally eligible. The difference would be in the amount they could borrow. The single person would be likely able to borrow more due to less income tax liability.

Depends on if the couple has kids and how many. The bigger the family, the larger the expenses. 40k goes a lot further for a single person than it does for a family, banks calculate everything when approving home loans. So a family of 5 may only qualify for a loan up to say, 150k. While a single person may qualify for up to 200k... All about debt to income and expenses.

Whoever gets an accepted contract would get the loan.

What kind of question is this? Banks don't discriminate based on your marital status. LOL

And, if you are asking which one a seller might want to sell to...If everything else is the same, I would sell to whomever offered the most money and least concessions.