Are these names difficult to say for people who speak Spanish as their first language, and how would they be pronounced with a clear Spanish accent?
[name_m]Frederick[/name_m]
[name_m]Edmund[/name_m]
[name_m]Augustus[/name_m]
[name_m]Theodor[/name_m]
[name_m]Alfred[/name_m]
[name_f]Isabelle[/name_f]
[name_f]Eleanor[/name_f]
[name_f]Adelaide[/name_f]
These names would all sound very different pronounced in Spanish, except for maybe [name_f]Eleanor[/name_f]. There is no Th in Spanish, so it would be pronounced as if the h were not there. So [name_m]Theodor[/name_m] would be [name_u]Tay[/name_u]-oh-dor. [name_f]Isabelle[/name_f] should be easy enough, just say it’s pronounced like [name_f]Isabel[/name_f].
I’m not Spanish but I have studied the language and I have Spanish-speaking friends.
I think [name_f]Eleanor[/name_f] would probably get pronounced as el-eh-ah-nor by people who are not familiar with the [name_f]English[/name_f] pronunciation. And the H in [name_m]Theodor[/name_m] would be silent. [name_f]Adelaide[/name_f] might be pronounced like ad-eh-LY-deh. The rest, I think, would probably be okay, but they would definitely be pronounced with a Spanish accent. So [name_m]Fred[/name_m]-eh-reek for [name_m]Frederick[/name_m], for example.
This response kind of solves my problem because I pronounce all the names you mentioned, apart from [name_m]Theodor[/name_m], in the Spanish way. Likely because I’m Finnish and vowels are mostly pronounced similarly in Finnish and Spanish. Honestly, I don’t even know how [name_f]Eleanor[/name_f] is supposed to be said if not el-eh-ah-nor…
I’ve heard [name_f]Eleanor[/name_f] pronounced “[name_f]El[/name_f]-len-or” in [name_f]English[/name_f]. The pronunciation you use sounds much nicer.
I see. Yes, I think these names would sound pretty similar in European languages.
Eleanor is typically pronounced EL-uh-nuh in [name_f]England[/name_f] (non-rhotic pronunciation) and EL-uh-nor in the United States.
*no th in American Spanish… European Spaniards pronounce my name which has a prominent th just fine, they just treat it like a c/z
Elinor might be a more viable spelling for Spanish speakers, I would assume.
[name_f]Isabelle[/name_f] & [name_f]Adelaide[/name_f] would be fairly easy, as they are names in Spanish as well. [name_f]Adelaide[/name_f] can also be [name_f]Adelaida[/name_f] in Spanish.
If they’re relatives, they might change them to their Spanish counterparts.
[name_m]Theodor[/name_m] would be [name_m]Teodoro[/name_m]
[name_m]Frederick[/name_m] = [name_m]Federico[/name_m]
[name_m]Edmund[/name_m] = [name_m]Edmundo[/name_m]
[name_m]Alfred[/name_m] = [name_m]Alfredo[/name_m]
[name_m]Augustus[/name_m] = [name_m]Augusto[/name_m]
[name_f]Eleanor[/name_f] = [name_f]Leonor[/name_f]
However, if you prefer the [name_f]English[/name_f] pronunciation, then [name_m]Augustus[/name_m] & [name_m]Edmund[/name_m] might be the only ones I see them having trouble with 
Frederick- FRAYED-reeck
[name_m]Edmund[/name_m]- AYD-moond
[name_m]Theodor[/name_m]- TAY-o-door
[name_m]Alfred[/name_m]- similar to [name_f]English[/name_f] pronounce but much lighter emphasis on the “d”, and the “[name_m]Al[/name_m]” is more like “Ahl”
[name_f]Isabelle[/name_f]- EE-sah-belle
[name_f]Adelaide[/name_f]- AH-day-laide
I’m not fluent in spanish but this is how my spanish-speaking MIL would say these names.
I tried. 
Thanks😄