Will I need to provide any proof that my husband and I do not reside at the same address when I amend from Married Jointly to Head of Household?

No proof is necessary. But to file as head of household you have to have a qualifying person.  This article has the details. 

https://turbotax.intuit.com/tax-tips/family/guide-to-filing-taxes-as-head-of-household/amp/L4Nx6DYu9

you can amend but the 1040-X needed won't be ready until 3/25.  then you should be able to file it electronically.   When changing from joint to MFS, you only have until 5/17/21 - the revised original due date for 2020 returns. 

@Mike9241 

Thanks for you response! I will be filing as Head of Household since I have children that live with me. 

Do I still have to wait until 3/25? 

@Bsch4477 

Thank you for your prompt response!

I’d like to confirm that I can amend from Married Jointly to Head of Household. Is this correct?

Yes. If you have a qualifying person as described in the article that I referenced you can file as head of household. You can actually amend your return to do that any time in the next 3 years. Only if you amend to married separately do you have to do that before May 17 but I understand that isn’t your intention. As mentioned, TurboTax will allow e filing of an amended return soon. 

@Bsch4477 

I understand, thanks!

I would like to know now what happens once we both amend. Will the IRS take back any refund or stimulus amount they have already given me?

For one thing, my last child was born in 2020, so I claimed the Rebate for him. However, now my husband will be claiming him. So does that mean the IRS will be automatically removing that from my bank account and giving it to him?

Also, will I have to pay back any refund? I believe I should be getting more, but I'd like to know this information before I use any of this money.

When you amend your return you will be dropping one child from being your dependent so, yes, any stimulus for that child given to you on your original return will be deducted. Note that since the child your husband will claim lives with you, you can still get earned income credit and child care credit for that child if otherwise qualified even though that child is not claimed as your dependent. You should give your husband a signed form 8332 to allow him to claim a child who doesn’t live with him. 

@Bsch4477 

I have two other children that are my dependents from a different father. My last child which my legal husband will claim, lives with him. Which is why I see it as fair for him to claim him. 

So the stimulus I received from the rebate will be deducted from my new return amount? Does this mean I will have to pay back taxes for the stimulus received if it surpasses any tax return amount I am due when filed as Head of Household?

I am worried this will complicate things once we start receiving those monthly payments in July (If I am correct)

Since the third child lives with him you could not claim that child unless he gave you permission to do so. 

When you amend your return you will be claiming the two children who live with you and will file as Head of Household.  As opposed to your married jointly original return you will be claiming one less child so will have one less child tax credit and if you claimed the stimulus for that child  originally your return will no longer include it.  If you claimed earned income credit originally it will be less on the amended return since you have one less dependent. The positive side is that what you get you keep as opposed to splitting any benefits with your husband. 

the stimulus is not taxed, it is considered a payment, so removing the stimulus in the amendment will adjust things by exactly $1100.