Problem In Our House Because Of my Brother's Girlfriend

A young man needs advise, he said his brother's new girlfriend is tearing their family apart:

I have two siblings, including me we are 3 altogether and our mom is late, so the three of us stay together in one house we built together. 

My brother has a girlfriend that spent a week with us this month and the first day, she was kinda sluggish which I hate like waking up around 7am and staying in bed till 11am.

As expected, when you go to people's house, you do what they do...

If they use only maggi to cook, you don't add your own seasoning, even if its not your boyfriend you're expected to do what they do and assist in every chores they do. 

First night she cooked, she used something like onga to cook although it's not onga which purged me during that week but I endured. 

And she cooked "ewedu" that we don't eat at home, my brother never eats ewedu, but he ate it because of her, I was really shocked because even if he's hungry, he'll never eat ewedu soup, but he ate it. I just assumed that it's love and I cleared it from my mind. 

Until last week, he fought with my sister and punched her because she wasn't happy with his girlfriend and she was giving her attitude. Even me, I'm not happy with her, but I don't show it, but she showed it because she can't take it, so he punched her and she started bleeding profusely on her nose, and that was the first time I would see them fight.

That's not the end, he got her a new Phone, meanwhile my phone's touch pad is bad and he hasn't even said anything about it. 

Seriously guys, I'm angry and sad, I think this is getting out of hand already. 

And he'll be asking me every time that "do I like his girlfriend?" But I really don't have an answer because I don't want to break his heart, I really don't have an answer for him because I'm not happy with her vibe at all. She's bringing badluck to our peaceful family.

Please what do you think? Should I tell my brother the truth?