I am really surprised that the vets didn't recommend neutering them - it's usually quite the reverse. A friend of mine didn't have her tom cat neutered and he actually almost wrecked her house, and became quite a nasty cat. She was advised to have him neutered and he turned into a totally nice, well behaved young fella and became all loving and friendly again!
If you are keeping cats as pets and don't want kittens then it is always advisable to get them neutered, both male and female. I believe that neutering is recommended for tom cats at between 6-9 months, depending on what the vet feels is best.
Yours are well overdue for the chop. Don't worry, it's only a small op and doesn't affect them too much. A week or so for their hormones to then settle down and you will find the problem will probably go away completely.