confused !! maintenance sux.. not really..pics
If you are happy then keep it moving. As long as your doctor is not sounding any alarms, I would not worry. 
If you are comfortable in your body, that's all that matters.
People who have known you for a long time are still used to the larger version of you. I would bet that to them it feels like you are too skinny to really be that old you. Maybe they're afraid that who you are has changed along with your size. As time goes on, they'll start to associate this new size with you though, and it won't seem so unfamiliar and strange to them.
As far as your sister's comment, everyone has different aesthetic preferences when it comes to bodies, but her 12 year old boy comment was totally out of line. She may find curvier bodies more attractive than lean bodies, and that's fine, but no one should push their own preferences onto others like that. What's most important is that you are comfortable and happy with yourself, not that you fit into anyone else's ideals of beauty.
Not that my personal opinion should matter, but I think you wear your current weight very well. You also seem to possess a slight hourglass figure, which is generally considered to be highly feminine and attractive. So that no curves comment is blatantly false.
I also think it's really important to love your body, and its appearance should be one of the least important things as far as that goes. What can your body do for you now that it couldn't at the beginning of your journey? In what ways does it enable you? Bring you happiness and pleasure? What amazing things have you done and can you do with it? As far as this goes, too skinny would mean you don't have the strength or the stamina to do the things you want to do with your body. If your body makes you feel strong, capable, and confident, then it's absolutely perfect. Don't let anyone tell you otherwise.
If you want, you can tell anyone who comments that you feel healthier and more energetic than you have in a long time, that you feel comfortable and happy at your current size, and that you appreciate their concern for your health and wellbeing but you can assure them that you are focused on giving your body the nutrition it needs to remain healthy and fit. That's really all that should matter to them.
Height: 5'0" HW: 289 SW: 279 
Next Goal: under 250 lbs
I looked at your photos, you do not look too skinny. You look normal. They are pick one or more...1) jealous, 2) not used to seeing you thin and need time to get comfortable with you looking normal, 3) used to seeing people in their environment that are heavy ( no one in Europe or Asia would ever think you are too thin). 4) Did I mention jealous???
You look fine, and for now, maintaining this weight seems easy. It might get harder later, most people gain not lose with time. I used to have the same thoughts as you...not anymore.
