What was the closing date in the original contract and why would that need to be extended - your last sentence. If you're intimating that you are looking to extend because of the vacation and they are unwilling, well then maybe you have a problem. If you planned around the vacation and they want to move it up, different story.
Nothing sticks unless changes are acknowledged and signed by all parties - but that last sentence has me curious....
Joshua is right, all that really matters is what you signed in the original purchase agreement. If you signed a GAR form used here in Georgia, look at item 6 on page 2 of your agreement. It is very specific about your closing date. You do have one 7 day extension which you can file notice to the seller without getting their approval, but this is only allowed if your lender can't complete the mortgage docs in time, or if the closing attorney finds problems with the title (liens, etc. on the property). Otherwise, if you must change the agreed closing date, then both parties must agree in writing. You wrote "the seller moved up the closing date to March 21" - they cannot do this unless you AGREED IN WRITING. If you did not sign anything saying you agreed to moving up the date, then they are just blowing smoke and cannot rescind your offer without being liable for damages. Did you sign any other special addendums with Home Path that possibly gave them the right to make unilateral changes? In any case, these are all questions for your agent - remind them that they work for you, and have them explain why they are trying to move up the closing date if you never agreed to it in writing.
I must admit that I'm curious as to why your Buyer Broker is pressuring you rather than working to resolve the problem. Frankly I doubt the home is going to get sold between March 21 and the frost week of April and honestly were I your broker (I'm not nor am I licensed in GA) this would have been resolved long ago.
The listing agent works for the Seller, and is simply repeating whatever the Seller says regardless of whether it makes any sense or not. Your agent works for you and I'd would remind them of this strongly. I would advise both agents in writing (email is considered writing) that should your earnest money be touched without your written permission you will be filing written complaints against both of them and both their firms with the GA state real estate commission.
If you did not sign any papers agreeing that the closing date was to me changed to March 21, then I'd tell my agent that they are on very thin ice and that if they do not get this resolved in the next 24 hours that you will be taking legal action against them and their office and have already prepared a written complaint to be sent to the real estate commission. That you expect them and their office to represent your interest and only your interests and that you are not feeling that they are. Get the names of and speak to both agencies Broker in Charge and let them know you expect this to be resolved today.
By the way, you are not blameless. You are buying a home and should be focused on this and paying attention. Whenever you sign something and send it to your agent you should expect an acknowledgment that they received it and if it requires another signature from someone you should receive it back signed within 72 hours and if you don't get it you should be on the phone and demanding to know why. If you were unhappy with the Sellers refusing to make any concessions after your inspections, you should have canceled the deal right then and there. It does not sound to me as if you are focusing on the transaction, you certainly aren't getting good advice and you are waiting too long while you hope the problems solve themselves, which they won't. It sounds to me as if most of your problems could have been easily avoided by paying more attention and by engaging an attorney in the process early on.
Most of what you wrote in your question is unfortunately completely irrelevant. The only thing that matters is what was signed by all parties.
If you signed paperwork that says you will close on the 21st then, you should close on the 21st. I'm assuming here that you wouldn't have signed this KNOWING that you had a vacation planned.
Assuming you didn't sign something that put you in this position (meaning you didn't sign it thinking you could change it later), then tell your agent to be a Man(or Woman) and start representing you.
Let's review the market.
Are there a ton of buyers buying foreclosures, YES... but...
Is there another buyer that can close as quick as you can (meaning before you get back from vacation)... NO
There's also not a lot of buyers in Covington right now either.