I’m not sure if you can ask for a refund of the green card fee under the circumstances. But derivative status is entirely dependent on the principal entering the US before or with the derivatives.
When traveling to the United States, the primary (or principal) applicant must enter before or at the same time as derivative family members with visas. A visa does not guarantee entry into the United States.
https://travel.state.gov/content/travel/en/us-visas/immigrate/the-immigrant-visa-process/step-10-prepare-for-the-interview/step-12-after-the-interview.html
Top 10 Mistakes at Visa Interviews
The Visa interview is the most important part of the whole visa process. A successful interview has a positive impact on your visa being granted. Following are some of the most common mistakes people make during their interview.
1. Not Prepared Well for the Interview Being prepared for interview can better equip you for the interview. Prepare beforehand for commonly asked questions and their appropriate answer will be helpful prior to the interview.
2. Not Providing Complete and Truthful Information It is very important that you provide complete and truthful information. Any incomplete/false information can lead to unnecessary delay(s). False information can have severe impact on your future ability to apply for US visa. It may also cause you lot of frustration and legal actions against you. You could be band for life from receiving a US visa. THINK before answering.
3. Providing Incomplete Documentation Prepare all the required documentation with complete and authentic information. Read all the prerequisites and prepare all the documents accordingly. Keeping your documentation well organized can also leave to a positive impression on the consulate officer.
4. Not Carrying Appropriate Fee US consulate has strict methods of payments. Make sure you know the method and the exact amount of the applicable fee. For example, most US consulates don't accept cash as the payment method and would prefer separate bank drafts for visa application and visa issuance fee. Refer to an appropriate source for more detailed information. (most fees are paid upfront, but...)
5. Providing Unnecessary Extra Information Do not give away any information voluntarily which is not being asked. In many cases, people trying to be over confident and over smart give out more detailed answers than is required. This may trigger additional related questions which may not work in your favor.
For example: Question: Why do you want to go to the US? Wrong Answer: I want to see how USA is and if I like it I want to stay back with my son. Preferred Answer: For tourism purpose and/or to spend some quality time with my son/daughter.
6. Inconsistent Information Inconsistency in the information about what you provide in the documentation and what you say during the interview can go against your case.
7. Arguing with the Consulate Officer Never ever have an arguments with the consulate officer. If you want some information ask in a polite manner.
8. Having Poor Communication Poor communication is the number one reason that can affect your case in a negative way. If your English is not that great, then you should request for a regional language interpreter. They are offered at the beginning of the interview.
9. Having too Much Communication (talking too much) Remember, you are the one being interviewed and not the other way around. So, keep your communication brief and to the point. Speak only when asked for an answer.
10. Appearing to be Nervous Being confident can bring positive results. Especially, in case of visa interview where a consulate officer has to rely on limited information provided by you. Their judgment is highly influenced by the way you react to questions, your body language, and the authenticity of you answers.
It's definitely something you can request although whether it gets approved seems to be the luck of the draw.
I've had conversations with a few who managed to get it through based on start date but they were in healthcare.
Also based on current estimates you should recieve your interview appointment date this month with your appointment being in April.
I would suggest booking your medical now so that it doesn't cause additional delays when you do get an appointment as the medicals are fully booked about a month in advance.
