For 24 in CH2 you needed to tell him you like boys/him, picked his group, asked him to runka during the 2nd camp choice and do a succesful blot ritual with him. In CH3 you have to pick "I'm not a child anymore" when he says he'd take the medicine to alpines and then lock your romance with him.
25 at the end of CH3 if you romanced him.
26 when you meet him at Alfheimr if you romanced him.
34 and 35 are also romance only, you have to pick him when you get the Ancient Strategy mission. The scene should trigger the 2nd time you talk to him after defeating the Fenrir Mother.
Erland 22 - During the party at the end of CH2 give water to Njal, Asbru to Yrsa, take the huldra essence for yourself. Give Erland cigars, beer and fine booze until the party ends. If you have at least 40 affection you'll get a new choice, pick option 2 or 3. 3 gives more points.
Tyr 17 - In CH3 pick practical clothes for him, you should get a variant of the scene at the pool table if you pick his romance option, you'll need at least 30 admiration.
Asshole gives you a Manaz(T3) relic. Val or Alfrothul gives you an Uruz(T2) relic.