TSH can vary significantly, even intraday. Some say it varies as much as 70% from highest to lowest, so even the time of day the blood was drawn can affect it.
FT4 is more important, and your is perfect, right at midrange.
Low vitamin D can cause many of the same symptoms as hypo. Make sure your D is well up in the range.
Your TPOab is, as you say, just slightly elevated, and that can happen in a number of conditions. We often see TPOab numbers in the hundreds or even thousands. So, I would consider yours borderline.
Since your brother has Hashi's, it would probably be a good idea to continue to monitor TPOab to see if an upward trend is developing. Have FT4 tested when you have TSH tested. If FT4 goes much below midpoint of range (1.3 on your current range of 0.8-1.8), it could start causing symptoms.
t4 free range is ( 0.8-1.8 normal range) my results were 1.3. My throide peroxidase ab was only 59 but (normal range is <35). I am just curious bec. I was low with vit d and I am taking vitamind3 & it is normal now still take supplements. Then I am PCOS & my total testorone borderline high & I am on medication. I struggle with losing weight. I just find hard to believe my tsh can change that quickly.
What's your TPOab level and the reference range? Elevated TPOab is usually a marker for Hashiimoto's, but it can also be elevated in some other conditions. What's the reference range on your FT4? Ranges vary lab to lab and have to come from your own lab report.