Be calm and be careful. Cats are hard to restrain. You must adjust your attitude. The best option is to try to restrain as little as possible. Don't try to restrict the cat's tail.
Cats use their tail to dissipate tension by swishing back and forth.
Just try to work around it. Cats seem to have a remarkable sense about who likes them. It is especially important that you perform these procedures in an unhurried manner, and that you don't get stressed out yourself. Talk in a soft, soothing tone of voice, stopping occasionally to stroke the cat's body. If your cats are particularly high strung or nervous, there are a couple of all-natural calmatives or tranquilizers that might help.