Can we file a tax return if we have not in the last 2 or 3 years?

Yes you can file a tax return if you have some taxable income to enter.  Each tax year has to be prepared separately.  You cannot combine income for different tax years on the same return.  What tax year do you need to work on?  What income do you need to enter?

Yes you can file a 2019 tax return even if you have not filed a prior tax year.  However, if you have a tax refund the IRS may hold your refund until you file for the prior years.

If you think you need to file a tax return for the stimulus, then there is no need if you do not have any income to enter on a tax return or you only receive Social Security benefits and are not required to file.

If you only receive SS benefits then the stimulus will be deposited into the same bank account as your monthly SS payment.

If you do not receive SS and are not required to file a tax return then go to this TurboTax website to register for the stimulus - https://turbotax.intuit.com/stimulus-check/