Sorry, but I think "find familiar" on a ranger makes no sense.
I have not played a 5E game before, but judging from the previous games:
Familiars are small pets of casters ( mostly wizards, in pathfinder also witches) that give their owner minor bonusses, help them with spells or do stuff for them like scouting or delivering messages. They are not well suited for fighting.
In a video you saw Swen summoning a little spider that was killed when attacking Shadowheart. Thats it.
Rangers should have an animal companion.
I do not know much about 5E, but it would be cool if a ranger could charm an animal to become his companion instead of using a summon spell.
This could cause you trouble if the animal already has an owner or it is part of a group of animals.
Imagine you start as a lone ranger. Then you meet somebody riding on a horse. You charm the horse, the owner gets angry but you and the horse kill him together.
To avoid some cheese, charming might take some time and require concentration and you have disadvantage when trying this during combat.
1. Find familiars don't give bonus in 5e. They are normal creatures with the basic animal stats they represent and have their own initiative. They are useless for combat outside for pulling lever and stuff like that.
2. The find familiar has nothing to do with the animal companion. If you want an animal companion you have to pick the Beastmaster archetype at level 3 (in the PHB). But we have no idea how it will work in BG3 because Larian isn't implementing the PHB version of the Ranger.
3. Charm animal is a spell, no relation to animal companion either.
