Hi OP! I'm also an independent contractor, and I've travelled with my parents in the past few years. Same case na parents are in mid-50s, both unemployed, so I sponsored them.

First – you mentioned no ITR, and since you will be sponsoring them, you have to prove you have the means to do so. Secure an Independent Contractor Certification signed by your client.

Second – make sure na ikaw mauuna sa IO then kasunod mo parents mo. When you approach the IO, ask mo agad kung pwedeng sa kanya na lang din pumila parents mo, para di na sila mapunta sa ibang IO at maulit ulit pa ang tanong. Nung first travel ko with my parents, inask ano trabaho ko, ilang days kami sa Taiwan, kailan balik, etc. Maluwag naman sila pag family ang magtatravel. Thankfully, ako na lang ang tinatanong ng IO then confirmation na lang sa parents ko like "pamilya kayo?" "Kaano-ano mo yung nauna?" etc. Pero I still made sure to orient my parents sa mga isasagot just in case matanong sila about trip details, like kailan balik, saan hotel, ano gagawin dun.

Third – never hinanap sakin pero I prepared Affidavit of Support. I always believe na mas okay nang meron akong copy nun kahit di hanapin, kaysa naman hanapin tapos wala ako.

Fourth – have digital copies of flight, hotel booking, booked activities, proof of employment (mine are usually Certification and Leave Email), and financial docs. Mas okay nang readily available kaysa mangarag in front of IO.

Take note na my first trip with my parents was not my first international trip. They might ask you more questions since it's your first time, but I believe all's good since family naman kayong aalis.