I'm quite new here, and I've never had 2 dogs at a time, but my mum's friend does.
She has male Golden retriever (GR) for some years and it's always good and tamed, that's why she decided to get a male shih tzu (ST) last year, both of them couldn't get along, GR hates ST and ST hates GR. They fought everyday, at first she just let them fight, naturally the one who wins in fight will become the leader, this was what she thought.
But after a while it didn't work out because there were times her GR bitten off the ST hairs and hurt it, the ST often injured and bleed. She decided to separate them, and place them together only under her supervision. She didn't give up in trying, she took months in trying
Until a day (recent months), my mum got a call from her friend, my mum's friend was admitted to the hospital because her GR intended to kill the ST, GR actually locked ST throat and the ST nearly died, so she used her hands, fingers to force open her GR's mouth and wanted to let ST go but the GR wouldn't allow, and actually bite even harder, she tried and tried until her index finger was bitten off by her GR! The bone cracked and her fleshes came out, the GR got very scared to hear his mum's scream and finally let the ST go!
So now, this friend of my mum lost 1/2 of her index finger and stopped the fight between her GR and ST. But sometimes they will still fight, but unlike previously.
I met her that day, she admitted it was definitely a horrible experience for her, but she still loves her furbabies, she told me
I didn't mean it's bad to have 2 dogs, because I still see a lot of people have 2 or more dogs and they get along well, I was just telling what I saw, it really much depends on the personalities of each furbabies, your furbabies are both young and I think they would be OK if you spend more time with them.
Best of luck, keep posting!