Neutering will DEFINITELY help. And let me applaud you for rescuing these guys. Male cats can be extremely agressive if they are intact. They will also usually spray and are not very good companions for indoors until they are 'fixed'. It takes about 3 to 4 weeks after neutering before you will see a marked improvement in your boy's attitude. If he is a sprayer, and continues to do that after neutering, you may also want to talk to your vet about putting him on medication such as Buspar for a few weeks to see if that will help with the inappropriate marking.
Please let me know if I can help further.
Feline Healthcare
16 yrs health care mgmt & issues relating to cats, reproductive issues and multicat environments