Yes at the same time but Not together. You have to print and mail amended returns. Mail each year in separate envelopes or the IRS might miss one. Get a tracking number from the post office so you will know they got it.
No. Do not put them in the same envelope if that is what you mean. Prepare and mail each one separately or you run the risk that whoever opens the mail at the IRS will overlook or throw one of them away. Amended returns must be printed, signed and mailed. They cannot be e-filed. Each tax year's amendment (Form 1040X) is a separate return.
A 1040X cannot be e-filed. It must be printed and mailed. It will take about 3-4 months for the IRS to process an amended return. It is a good idea to use a mailing service that will track it, like UPS or certified mail, so you will know it was received.
Wait about 3 weeks from mailing and you can check the status of your amended return:
https://www.irs.gov/Filing/Individuals/Amended-Returns-(Form-1040-X)/Wheres-My-Amended-Return-1
https://ttlc.intuit.com/questions/1908543-do-i-need-to-amend
https://ttlc.intuit.com/questions/2566895-what-does-it-mean-to-amend-a-return