My daughter recently rented a house. The heat in the house blows cold air in two of the bedrooms and one vent in the dining room. The landlord is telling her these are return air ducts. If this is the case half of her house has no heat. Is this possible, there are what appear to be two return air ducts in the bathroom. This is a very old mobile home actually it is to mobile homes which have been put together to create a doublewide. One side of the home has no heat. I don't think it was ever hooked up. Thanks for your help

If two mobiles have been put together they should both have a furnace as the were originally equipped with one each

Sounds like the person who put these units together did a hack job. Usually one mobile furnace can only keep up with the heat requirements of that unit and asking one furnace to do both units will not work.

You need to have a talk with the owner to see if he is going to fix this problem.
I will warn you that heating a old mobile home is very expensive an doing two of them will break the bank.
Good luck.