So I'm trying to add some relationship types from the Parenthood GP to one of my sims. Here's a list of them:

Guided Child — A great relationship with a authoritative Parent.
Provided Happy Childhood — A great relationship with a relaxed Parent.
Respected Heir — The best relationship with an authoritative Parent.
Mommy’s/Daddy’s Boy/Girl — The best relationship with a relaxed Parent.
Obedient Child — A neutral relationship with an authoritative Parent.
Parented Passively — A neutral relationship with a relaxed Parent.
Repressed Child — A negative relationship with an authoritative Parent.
Unhappy Child — A negative relationship with a relaxed Parent.
The Best Lil’ Boo — A great relationship with a Grandchild.
Grandkiddy — A neutral relationship with a Grandchild.
Grumpchild — A negative relationship with a Grandchild.
World’s Best Grandpa/Grandma — A great relationship with a Grandparent.
Plain Ol’ Gramps/Gran — A neutral relationship with a Grandparent.
The Grumps — A negative relationship with a Grandparent.
Grateful Guide — A great relationship and a lot of discipline.
Happy Childhood — A great relationship and little discipline.
Oh Captain, My Captain — The best relationship and a lot of discipline.
Daddy/Mommy Dearest — The best relationship and little discipline.
Commanding Presence — A neutral relationship and a lot of discipline.
Passive Parent — A neutral relationship and little discipline.
Punishing Parent — A negative relationship and a lot of discipline.
Unhelpful Parent — A negative relationship and little discipline.
Thick as Thieves — A great relationship with a rival sibling.
Super Siblings — A great relationship with an ally sibling.
Family Frenemy — A neutral relationship with a rival sibling.
Childhood Buds — A neutral relationship with an ally sibling.
Childhood Tormentor — A negative relationship with a rival sibling.
Childhood Enemies — A negative relationship with an ally sibling

I've tried using traits.equip_trait to no avail. Can anyone help me with the right command?

I don't know of a way to but that console command is only for traits. I don't know of a way to use a command to edit a relationship besides MCC (but I don't recall it having those options you're looking for)

They would most likely fall under the relationship bit "rel.bit" category. If you have debug cheat access available in your game, shift-clicking on a sim displays all the relationship bits options you can add or remove from a sim. But a word of warning, it is known to be a problematic cheat, one of the ones Maxis probably would advise you against using. (Especially after Seasons patch and the removal of many debug cheats.) Adding or removing rel bits via the debug method can render a sim unplayable, such that their particular family (Single sim or multiple family members) will never finish the loading screen if you try to play the family after diddling with their rel bits. So certainly save before experimenting.

you can just shift click as coolspear1 said. However, you're going to have to add relationship bits for both the sims (ex. parent and child) Otherwise one sim might view the parent as "mommy/daddy dearest" but the parent does not have view or special relationship with the child. (that's what happened to me)

Indeed, as CupcakeWitch advises, you have to give/remove both sims in the relationship the appropriate rel.bit. Also, many direct familial relationships do not even show in the Family Tree when doing it the cheaty debug way. So even if it does not break the family to be unplayable, you might not like the end result of it being unregistered and ignored in the Family Tree.

Thanks for the info guys! I think I'll leave it alone. Not worth the risk of screwing up my sims