I really doubt Barclay will have a problem with Baxter...it's likely to be the other way around. Understand at 3 years old...Baxter may not care too much for Barclay's puppyness. If he isn't interested in playing...he'll let him know. My Ramsey is three...she isn't always willing to play with Reggie who is 7 months. She plays with him on her terms...when she wants to. When necessary...I distract Reggie from bugging her.
If they play well together...you won't have to occupy them at all...they'll do it themselves. If you have a yard...I really suggest taking them outside... to do "dog" things. All of mine follow each other around the yard...
For feeding I suggestion two seperate bowls...not placed side by side...across a room. I walk three....best advice there...it helps if everyone is going in the same direction.