Thranduil and Oropher are Sindar and may be related to Thingol in some way. Presumably they lived in Doriath in the First Age.
Gil-galad is more complex. JRRT changed Gil-galad's descent several times (there is no 'canonical' statement by JRRT on this). While initially writing LotR Gil-galad was a descendant of Feanor (I do not think I have seen anyone support this version). If this had remained the case Gil-galad would be a full blood Noldo. Later he became the son of Fingon and grandson of Fingolfin (this is the version in the Silmarillion and Unfinished Tales. Christopher Tolkien implies that this is what JRRT had in his geneological tables and did not change them. Most people seem to prefer this version). If JRRT had decided to go with this version Gil-galad would likely be about 88% Noldo and 12% Vanya (presuming Fingon took a Noldo wife). Later Gil-galad was the son of Finrod and grandson of Finarfin. In this version Galadriel is Finrods daughter (I dont think have seen any arguments supporting this version). If this had been accepted Gil-galad would have been half Sinda (if Finrod took a Sindarin wife), a quarter Teleri, an 8th each Noldo and Vanya. If Finrod took a Vanya to wife (ie Amarie) then Gil-galad would be about 2/3rds Vanya, a quarter Teleri, and the rest Noldo.
The last version JRRT had before he died was that Gil-galad was the son of Orodreth (who previously was the brother of Finrod and Galadriel, but in this version now becomes their nephew) and great grandson of Finarfin (this version is argued for by some, but not a majority, AFAICT, of those interested in such things). If JRRT had decided that this was going to remain the 'true' version then Gil-galad would have likely been half Sindar and a mix of Noldo, Teleri and Vanya. We can all be thankful that JRRT did not change his mind yet again before he died;). (Then again something might still come out in his linguistic works)