I've heard it said that lambs will ruin a goats udder and that it's alright for them to suckle direct, don't know which is true.
I partly raised lambs on goats milk last year. It was ok when I just had a couple but then was given 6 and had to introduce some lamlac. One lamb wouldn't take to it, got the squits and after a week of trying I had to put him back on just goats milk and the rest on half and half.
He's still a scrappy thing and when the grass starts growing if I can ever get weight on him he'll go for meat eventually. His twin is slighty better. But those two were orphaned at birth the rest have done well but had 4 days on their mums first.
Goats milk isn't a rich as sheeps milk.