To check whether kanji are currently in use, you should use a Japanese native language dictionary.
I looked your words up in goo's dictionary (https://dictionary.goo.ne.jp/jn/147982/meaning/m0u/), because I was unfamiliar with both 具に and 備に.
If you look at their entry, it's written like this:
The x means that the character 悉 is not part of Joyo orthography (Government-mandated usage).
The down-triangle means the reading of the character is not approved by Joyo orthography. (Both 具 and 備 are characters in common use, but the reading is technically not approved).
Joyo doesn't seem to absolute dictate usage on the ground, but as a non-native speaker, I assume unless I frequently see otherwise, that one should not write things with the ▽ and that Japanese people will not even recognize x kanji.