You do need to file a bankruptcy as soon as possible to stop that September 7 foreclosure. Keep in mind that some attorney's offices may not be open on Monday the 6th due to Labor Day. The Chapter 7 will stop the September foreclosure, but not a later foreclosure once the lender is granted a "Motion for Relief" from the automatic stay. This means that the lender can then re-start foreclosure, which in GA means advertising for 4 consecutive weeks and a sale on the next available "Foreclosure...
A bankruptcy (Ch.7 or 13) may be reportable on your credit history for ten years. Successfully completing a Ch.13 though shows a reliable payment history and is a positive thing. The Ch.13 to address tax issues is a great recovery tool. You should consult with a bankruptcy attorney who can provide you greater detail as to how a Chapter 13 can benefit you and your situation.
Yes, as the others have said, the deadline for answering is something to be aware of. In Georgia, this is generally 30 days from when you were served. If you are having other financial problems, you may want to consult with a bankruptcy attorney as a filing would address these issues as well as the lawsuit. Most bankruptcy attorneys offer a free consultation. You do not want this lawsuit to turn into a default judgment and then a garnishment, as that will cost you more than just the $300.00...
The answer to as if you will loose the house depends on how much, if any equity is in the house. If there is little or no equity (less than about $10K) then if you continue to pay the mortgage you should have no issues. Refinancing to get the mortgage in your name may be required by your divorce decree and that will depend on your credit, employment, etc. but your ex-husband's Ch.7 filing shouldn't impact that issue.
Ms.Eliot is exactly right as to what to do, but I would like to add that you can expect the law firm representing the HOA (or the HOA itself, if they are self-represented) to be very aggressive and to try to seek additional fees at every stage of this process.
Mr.Zinn is correct as to your course of action. Most GA bankruptcy lawyers offer free consultations. If it has been more than 30 days since you were served with the lawsuit, the creditor can get a default judgment and then begin collection actions. A bankruptcy, particularly a Ch.7 can protect you and what is in your account that belongs to you, as well as stopping the lawsuit.
This is not really a bankruptcy question, but one best put before an immigration attorney. What does and does not impact your I751 petition is generally something that a bankruptcy attorney might not know, but your immigration attorney should. There should be communication between your bankruptcy attorney and immigration attorney as to timing and impact of your possible Chapter 7 filing.
Your ex-husband can file a Ch.13 to pay back the child support arrearage through the bankruptcy plan, but he must also pay his monthly obligation on time from the date of filing going forward. The bankruptcy doesn't alter his obligation to pay, it just provides a plan for paying the back child support.
One fact that isn't mentioned is if your mother has a bank account, which could be subject to garnishment from a judgment. It would be a good idea to consult with a bankruptcy attorney in your area, as she may benefit from a Chapter 7, which would address her credit card debt and any concerns about lawsuits.