You already got great advice from
Maximo, but just wanted to share that I experienced the same thing too! It's 'normal' I guess and each first dog will take a different amount of time to transition and accept the new puppy.
On our first day home, Scottie
hated Casie. And, he hated me! After I held Casie, he refused to let me touch him. I would just reach to touch his paw and he'd pull his paw back! I was so shocked at how mad he was. It was cute and sad at the same time.
Lucky for me Scottie doesn't hold grudges for long and was okay for me to touch him the next day
. It then took about a week for Scottie to accept that Casie was here to stay. And then another two weeks for Scottie to start to like her. And then another week to start to play with her. It's been about 3 months since we brought Casie home and they are playing each day and enjoy each other's company, but Scottie still doesn't allow Casie to be near him when he's sleeping.
I agree with Maximo, the training of the two together works wonders. I think this is the best way to regain trust. I think the reasoning is that both learn to respect you as the leader. Scottie and Casie learned how to take turns (i.e. tell Scottie to "sit" and treat; then, tell Casie to do a "sit" and treat)! It can be very cute when they learn to be patient and wait. It may take a while though...so be patient. But always command/treat Ted first! I always throw in a "good girl wait" - so she now learned the command "wait".
For the feeding issue - I started to feed them together in the same space and watch them eat. When I fed Scottie first, and he was done and had to watch Casie eat afterwards, he'd get jealous - even though he already just ate! So I decided to feed them at the same time and made sure to supervise them. Anytime Casie tried to sneak over to Scottie's dish, I gently pushed her away and back to her dish. She's learned now that she gets her own dish and is not to take from Scottie's dish. I always say "good boy eat, good girl eat" while they eat - they've now learned the command "eat".
As for holding the dogs - I would hold and pet Scottie first and look at Casie while saying "good girl Casie" and then I would hold and pet Casie while saying "good boy Scottie", giving him visual attention (he loves eye contact with me).
Try to
always give Ted the attention/petting/command/treat first. I know it sucks for Boss, but that's just the way it has to be as a second child lol. Just think of it this way - Boss never ever was the first child so this has and will always be the 'way it is' to him. As in, he won't know any different so he won't actually be hurt. Try hard not to feel sorry for Boss or both Ted and him will feed off your emotions, as if something is wrong and that's how the feelings of jealousy might continue on.