@Mkaren,

You may want to consider this. If your father converted to Islam and got married to a Muslim woman here, then he and his other wife is legally married in Qatar. But his obligations and responsibilty to you as a daughter still counts.

With regards to buying properties in Doha, yes it is possible for an expats but only in a certain areas.

Also, I never heard yet any agencies to contact for tracking down properties of a certain individuals in Qatar. I doubt if the authority will take concern in your father's case. Its not a criminal case though. But I think the best place for you to seek assistance are POEA, DFA or OWWA.