Morrigan having a son, How to customize?

All those options (romance, Morrigan having a baby, and who she has it with) are in the companions section of the DA: Origins section of the Keep.
Unsure what you mean about the marriage. If you want a warden King/Queen, you have to be human (as only a human noble had that option in the game). A female Warden could (under the right circumstances) be King Alistair's mistress, if that's what you're after? 

If you lock your choices after you make them, it will pop up and tell you what it wants to change if you make an incompatible choice later. 

Hi, i mean that I could only see the results of Morrigan in 'Battle of Denerim' I romance Zevran and I am a female Elf warden but the tapestry insisted that if I chose loghain killed the archdemon, then Morri becomes single.

when i googled had seen other players encounter this glitch too. Has Bio come up with a solution?

If Morrigan has an old god baby, you have to choose that the Warden kills the archdemon (as they game just makes you do that automatically when nobody's going to die from killing it, which was the whole point of the baby). Telling it that Loghain killed the archdemon is telling it that Loghain died, which means he can't have impregnated Morrigan. Computer logic 😛