for the German assets most likely German inheritance law will be applicable.
If there is no last will, you will not be considered.
Thus, it is of vital importance to make sure the last will is found and shall not disappear.
A common law partner under German law has no right of succession regarding his or her partner. This may be different if another law is applicable which is not likely but should be checked in detail knowing all assets and where your fiancee has been living.
With you fiancee being only a German national and his real estate assets in Germany, German law will be applicable.
This is why your fiancee should have made a testament and told you where to find it.
I don't understand how your German friends got to the conclusion that common-law partners would have a right under German law.
Generally due to his German nationality (if there is no other nationality), German law ist applicable for the succession, see Art. 25 EGBGB.
However, collision law of the other states you mentioned may cause that parts of the assets follow for example another law. This is particularly relevant for real estate assets,not bank accounts!
This is very complicated to find out and you will need a lawyer knowing the local law where the assets are situated.
If he had real estate in Dubai, you should look for a lawyer knowing Dubai law.
I am sorry, I don't have any idea about the Dubai succession law.
DISCLAIMER: Answers from Experts on JustAnswer are not substitutes for the advice of an attorney. JustAnswer is a public forum and questions and responses are not private or confidential or protected by the attorney-client privilege. The Expert above is not your attorney, and the response above is not legal advice. You should not read this response to propose specific action or address specific circumstances, but only to give you a sense of general principles of law that might affect the situation you describe. Application of these general principles to particular circumstances must be done by a lawyer who has spoken with you in confidence, learned all relevant information, and explored various options. Before acting on these general principles, you should hire a lawyer licensed to practice law in the jurisdiction to which your question pertains.
The responses above are from individual Experts, not JustAnswer. The site and services are provided “as is”. To view the verified credential of an Expert, click on the “Verified” symbol in the Expert’s profile. This site is not for emergency questions which should be directed immediately by telephone or in-person to qualified professionals. Please carefully read the Terms of Service (last updated February 8, 2012).