Can co-owners of a property both depreciate a property each for 27.5 years?

Yes you each should depreciate only your share of ownership less the land value , land is not depreciated.

to complicate: one owner claimed all the expenses, depreciation, paid all bills for 25 years; i claimed nothing - reported nothing; what can I do now - if that partner reported 100% for 25 years - is all the depreciation taken?

and you just discovered this?  Is there a written partnership agreement?

if one co-owner claimed depreciation and rental income for first 27.5 years and the other owner reported nothing - can the other partner then after that point restart another 27.5 years?

no written agreement -

we are listed on the deed as joint tenants -

it is okay, i just want to clarify that it is okay for one co-owner to for 25 years to report total rental income, expenses and depreciation?

what's done is done - now what? can a 50% owner of a rental property claim 100% of all involved?

This is beyond the scope of a user to user tax forum that was created to deal with current year issues with the Turbotax program.
You should contact a local legal tax expert that would know all the particular of your individual circumstances.