If two definitive ovums are fused will they form an organism?
No, it is not possible. The reason is the genetic imprinting, which takes place on the parental DNA in the egg and the sperm. Here small modifications are added to the DNA which marks them as silenced. So some genes are expressed from the mother (while the fathers copy is not expressed) and vice versa.

There are even genetic diseases which are caused by imprinting. One example is the loss of a gene region on chromosome 15. Depending in which copy its lost, either the Prader-Willi Syndrome or the Angelman Syndrome occur. PWS is inherited via the father, Angelman via the mother. Another interesting article on imprinting can be found here.

If you combine two eggs, some genes, which are not imprinted in the father, will not be expressed in the developing embryo which will finally lead to death of it. However, researcher deleted the maternal imprinting in mice and mimicked the from the father and made off-springs from two mothers possible. This is something which is ethically very problematic in humans. The article can be found here: 


Birth of parthenogenetic mice that can develop to adulthood