Hi Eru,

If what you have is indeed P. edulis flavicarpa, I'm skeptical it can make it through a Northern California winter. P. edulis f. edulis (purple passionfruit, such as 'Nancy Garrison', Black Knight, etc.) would be a better choice, as it should be able to handle temps above 28 or so (guessing). Still it would be wise to protect it if it's expected to go below 30. Hybrids with both the purple and yellow forms in their background (Frederick, Red Rover) would also be better choices than P. edulis flavicarpa, although they may be a degree or two less hardy than the purple form. The purple or purple/yellow hybrids should be able to cross pollinate your P. edulis flavicarpa.

As far as putting plants together, one will certainly grow faster than the other(s) however I think this can be dealt with by pruning.

As far as space, one P. edulis will fairly quickly fill a 15 ft. long space within a year. I think you could squeeze in two, but you would have to do a lot of pruning.

If I were you I would buy an established plant in a 1 gallon pot--the purple form would be best in terms of hardiness, the hybrid best if you want bigger flowers and fruit. You could plant it and see what happens to the flavicarpa over the winter. You could also pick up a second plant now if you see one and keep it in a pot. Then if space opens up, or the other plant dies you'll have a spare. This might make sense if you have room for a pot somewhere just in case. I understand 'Black Knight' is a good one for a pot. If your nursery doesn't carry it you may be able to special order it.

i grow purple passion, yellow sunrise, giant granadilla and sweet calabash.

the purple and yellow grow and appear identical other than the fruit down here in tropical south florida.

the giant granadilla is a huge leaf and fruit variety that hasnt taken off yet and the calabash is struggling (ive since learned they like drier climates)