If I initially filed through Turbo Tax & they've already been accepted, can I still send in my amended returns to the IRS & expect my refunds to change on Turbo Tax also?

No, amended returns are filed on paper through the mail and it takes the IRS t2-16 weeks to process them.  Your original return will not change and the IRS will have processed that one long before they get to your amended return.

You should  wait until you receive your refund for the original before doing the amendment.  It's not a good idea to have two separate returns under the same Social Security number in the system at the same time.  It could slow down processing.

Amend instructions follow:

https://ttlc.intuit.com/replies/3288565