It’s fine to ask! It depends on how much (and which) canon and fanfic you have read, and how much you’ve read between the lines.

#Let’s talk about sex

I’d say they both defied definitions, but the short answer would be, mortal!Lestat loves who he loves regardless of their physical container, and mortal!Louis struggled with bisexual/homosexual desires.

Spoilers ahead:

Mortal!Lestat: 

I don’t want to try to assign a label like “bisexual” or “pansexual” bc there’s so many labels for orientation now and the definitions are confusing no matter how many definitions I read or how many times ppl try to explain the thing to me 😛

I’d say mortal!Lestat is romantically drawn to someone for their soul first and their physical accessories second. He’s had relationships with men and women, been physically attracted to both.

• He had a relationship with Nicolas, for sure. They kissed, they slept together, it was all heavily implied. I doubt vampirebaby!Lestat would have been stalking mortal!Nicolas if they had only been Super Best Friends 5ever.
• Lestat didn’t talk about long-term female relationships as a mortal, but that he bedded the village girls (I can’t find a reference but I’m pretty sure he mentions it).
• And he bedded one of the actresses in the troupe he tried to run away from home with: “That night, the actress who played my inamorata gave me her own very special and intimate accolades. I went to sleep in her arms…”
• He might have had a side fling with the female actresses in the Paris theatre, Renaud’s: “Send flowers for Jeannette and Luchina, the girls I had fought with the most and most loved,”
• In ToBT, mortal!Lestat beds a woman (non-con), and has a short but intense relationship with another woman, and returns to her to prove he was telling the truth about himself. She kicks his sorry butt out the door. 
• Also in ToBT, Lestat wages a campaign of seduction on David Talbot, who does not give in, despite a valiant effort on Lestat’s part!
• in later canon, Lestat is powerfully drawn to Dr. Rowan Mayfair and promises he’ll give her the Dark Gift. 

Mortal!Louis 

He really doesn’t talk much about his pre-vampiring life. Claudia asks him about sex and he tells her:

“It was something hurried, and … it was seldom savored … something acute that was quickly lost. I think that it was the pale shadow of killing.”

Maybe he didn’t want to hurt her feelings, since he knew she could never experience it herself. Maybe he really felt that way.

Personally, I headcanon that Louis might have had a little experience in being with men as a mortal, but Lestat’s the one who really pushed him over the edge. Alot of vampirebaby!Louis’ issues with Lestat could have partly been bc Louis was brought up in a religious frame of mind that meant homosexuality was sinful, so whenever he felt physical and emotional desire for Lestat, he hit himself with a wave of self-hatred 😛