Is it normal for people to act gay in threesomes?

So, we had a party last weekend, and all of the parents went to a bar/restaurant, leaving me, my sister, and another girl (let's call her lexi), who is a family friend and my sister's best friend, home alone. They are both really hot, and I've been wanting to have sex with lexi for a while. So, I went in front of them shirtless, showing off my abs, and Lexi wanted to feel them. My sister knew I wanted her, and came up to me and started feeling my dick, telling Lexi that me and her explore each other's bodies. Lexi was curious, and watched as my sister and I continued fondling each other. We starting to lick, touch, and arouse each others parts, and after a few minutes, Lexi was naked too, masturbating and licking her nipples. We started to have a threesome and it was great, but I noticed some lesbian actions between my sister and Lexi. My sister had licked Lexi to orgasm once or twice, and Lexi had licked my sister's boobs and fingered her. That would be like me giving a blowjob or handjob to another guy. is it normal in a threesome?

FYI my sister and I don't have actual sex. If you want to see how my sister looks, just ask, because she likes other people admiring her body.