1. Was the waiver of rights
a/ giving it to your mother
b/ or only concerning the handling?
If the first, you have given whole to your mother, so she do as she want with the new property too, because it's hers.
2. Do you mean the title say
a/ "Jane Doe, widow" *
b/ or your mother's name?
If the first, why wasn't your mother's name put at the title when it was changed???
3. "not sure now if she's "absolute owner" "
Well. If 1a then she is
but if 2a it ISN'T proven to the Register.
4. "or does my other bros still have rights."
If 1b, you have rights still NOW
if 1a, then you have rights AFTER you mother die.
5. " if she can loan this small property"
It depend of if the lender find the documents good enough.
/Some lenders will sure say No if it isn't your mother's name at the title,
/while some other lenders can find it good enough.
* OR does documents say "Jane Doe, widow of /your father's name/ " ?
Then it can be seen as COMPLEETE (although some unclear.) TOGETHER with some other documents showing that's same as your mother as for instance the marriage certificate.