Long stay after marriage (visa/resident/dependant pass?)

Hello members,
I would like to clarify some questions
1) children yellow card
I have 2 kids, father is ethiopian, children have Russian citizenship and I don't want to change it for them so only get yellow cards
1st child  was born in Addis and has Ethiopian birth sertificate with father's name in it
2nd child was born in Kenya, with Russian birth sertificate with no father's name in it
As I understand it will be no big issues to get card for Ethiopian born kid
2nd child, as I understand need to get father name  in original sertificate and then do all translation etc..and then apply
Am I right?
2) long stay for children
with yellow card can children stay in Ethiopia and attend school or they need leave the country every 3 months?
3) marriage
If I will be married with children father (I know the procedure) which kind of visa (permit) will I have? Or I should leave Ethiopia every 3 months and be back with tourist visa?
Are there any kind of dependend pass in Ethiopia to stay without leaving every 3 months?
Any rights to work or need to go for work permit as usual ?
Thank you for advices,
Unfortunately I could find any helpfull information through internet