Living with ill grandma (enphysema), and neurotic uncles. Too much work. How much it can take part of depression? Or the responsability is all mine?

As above. Living with older family and taking care of their need can be very demanding, however, some times it is needed especially if they have contributed to u when u were growing up. If the work is too much ask for help.
Hard call. Family should take care of family. The rule i always use is simple. I tell the family that when the living condition is such that there is a decrease in quality of life for the patient if staying in the home versus professional care, then i recommend help. This makes the decision medical and not about guilt. God bless you. Also remember, dementia is hardest on the family not the patient.