You have a perfectly fine dog boy at home. You have no need to pick up more random strays
Same goes for Atani who you can marry and get pregnant
Now to actually answer your questions:
Azyrran is the only planned extra companion that I am aware of, because, as Emerald has said, the current policy is to only allow proven writers to tackle the task of creating one and keeping them up to date, and besides Savin everyone is only allowed one.
In more encouraging news, Gwyn and Zuuzan both already have pregnancy content, and for the former it is one of the main drives behind her interactions with the player. There is currently no pregnancy content for Elthara, and I am not aware of any more being written atm. However I see no reason why a priestess of the Goddess of Fertility and Motherhood will be adamantly against making babies with the player, so at least it isn't off the table.
Marriage content with any of the three might be a trickier subject. Zuzaan and Elthara don't get too close with the player, and both are kinda married to their important magic related job and their craft. Gwyn might be all for marrying the champ if they are kind and reliable, but she probably won't go for it if Garth won't give you two his blessing - and you will always have to deal with her Daddy occupying quite a bit of space in her heart.