Sorry you are not getting some more replies. I will give you what I think and would do in your case.
If you rent property out it is investment property. Since you live in one of the units I would consider 100% of the income as investment income from the three units. You do not count your rent unless a Corp or LLC or partnership owns the building and you are renting from that entity. I would only use 75% of the expenses to maintain the building including interest, taxes, lawn care etc and report these and the income on schedule E. The $25,000 you asked about is the max you can deduct to offset other earned income and you may or may not have that much of a loss depending on you income and expenses and depreciation allowance. I would also deduct the balance of the interest expense on schedule A (25%) if the amount is enough where it is a benefit you over the standard deduction.
Disclaimer: I aint no darn CPA but have been doing my own taxes for years and I did not stay at a Holliday Inn Expess last night either. Hope you can use this.
Going with the 75%, the rent income minus all expenses (mortgage interest, PMI, maintenance, etc) I break even (let’s assume).
Can I still deduct depreciation?
With accelerated depreciation is 3.75% of the 75% of the building:
$450k x 0.75 x 3.75= $12,656
If so, can say that I had a $12k loss?
That is the idea behind depreciation. Keep in mind the recapture rules that I know little about. If you use straight line I believe you are OK but to use accelerated may be too much too soon and you may have to pay back some of the tax . CPA advice would be better here.