My wife and I have joining tax return. My wife has been contributing money to 401(k) from the company where she works, and i’m retired without income. So my question is can I use my own money from bank account to contribute to the existing IRA account? Can my wife also contribute money from her own bank account and claim tax deduction? Is the money contributing from the bank account considered after tax which is not taxible when widthdraw?
All of this can be answered with one answer: each person has his or her own IRA.
You can use your own money to contribute, but you'll contribute to yours only, not an "existing IRA account", which belongs to your wife.
Your wife may be able to contribute money from her own bank account, depending on her salary, and on how much she contributed at work. See the limits, below, down on the page under 2018.
The different IRAs do different things. A traditional IRA gives you a tax deduction, a Roth IRA doesn't. Below is a basic difference, to give you a choice.