What state?
My father died without a will and we filed a Letter of Administration for our mother so she could manage affairs, etc.
I assume you meant that "we" (who are "we"?) filed a petition for letters of administration. Right? Letters of administration are essentially a court order, so only the court can file them. Also, why didn't your mother or her attorney file whatever it was that was filed?
the kids had to sign off our interest in his estate
Why did they "have to" do this?
The land as well as the deed for the home is listed in both parents names.
Then it's probably not part of the probate estate.
Our mother is concerned and wanted to find out whats the best way to his name removed from ownership of the land as well the deed.
Depends on the laws of the unidentified state where the property is located and on exactly how the deed is worded. Also, "ownership of the land" and "the deed" essentially mean the same thing. Presumably, your parents bought the property (the land and the home built on the land are not legally separate) from someone who executed a deed that said he/she granted the property "To [Mom] and [Dad], as wife and husband as joint tenants" or "as tenants by the entirety" (or something else). That deed would have been recorded with the county clerk or recorder, and that would create a record of ownership of the property. That deed will never change (i.e., you can't remove your father's name from the deed), but we can't know what needs to happen next without knowing the state and exactly what the deed says.
Since she is administrator can she just transfer the deed as well as land ownership over to herself?
That depends on whether the property is estate property. As noted above, it probably isn't.
Since neither you nor your mother seem to have any idea how to handle this properly (and since you appear to be teetering on the precipice of illegally practicing law), I would strongly recommend that your mother retain the services of a probate lawyer.