Hi, I don't claim to have any advice but can tell you about our family's experience. My 10 year old was diagnosed 3 years ago with T1 and that made us more aware of our younger son and the possibility he might develop T1 also. One night he was bad with an asthma attack and was on prednislone to help control it. He went to the toilet about every half hour that night so we tested and found he had a BG of 20mmol (about 360mg). Initially they thought it was the steroids that caused the rise but they waited for them to clear his system and then ran tests and confirmed that our youngest also had diabetes. He never had any of the classic symptoms either, he only went to the toilet frequently that one night and never suffered from excessive thirst or weight loss. He was started on 2 units of lantus a day but even that was too high initially and it was dropped to 1 unit. He was on 1 unit for a year before going to 2 units.
It is now 18 months later and we have just had to introduce novorapid to all his meals now, but essentially he was honeymooning for that long period of time. His body is still producing some of its own insulin almost like a basal insulin, which helps. At first I was convinced that both us and the doctors had over reacted because his glucose levels were always normal pre-meal and even now they are good but two hours after a meal his levels rocket up, which is why we have now introduced the novorapid.
Don't know if this was any use but I wish your family the very best, let us know how you get on with the antibody tests.