[Lorraine]

These are dogs. Intact males or females will mark territory out of instinctual behaviour, nothing to do with housebreaking problems. They are a nuisance in a pet home and this is why it is a good idea to spay/neuter. Also, you run the risk of other health problems. In males, they can end up with testicle cancers, prostate gland cancer, urinary infections/cancers and believe it or not, rectal cancers. In females, left intact, you run the risk of pyometria (infection of the uterus which can be lethal) mammary tumours, uterine tumours and or cancers. I have seen these in younger dogs under 5 years old as well as older dogs that were left intact.
You also run the risk of your two males starting to fight with each if they get the whiff of a female in heat anywhere within blocks radius. If they get into a fight and you aren't right there, they can seriously injure each other or one can get killed. You can't argue instincts and you would be surprised at how viscious a toy dog can be when instincts kick in.
For spaying/neutering, choose a vet that is experienced with toy dogs so they know what they are doing with the anesthesia. They should be using Isoflurine gas to put them under. I very small amount of presedative is used but the Vet must know toy breeds to know how much. For extra caution, if you wish, you can ask they be hooked up to an IV during the procedure. This will often cause less trauma during sedation and will give a ready line if other measures are required during the surgery.
Neutering is not complicated and at the same time you can have the teeth checked for retained baby teeth and if they require cleaning that can be done a the same time.
Lorraine