The timothy grass is good. How old are the kids? I'd separate and wether the buck at 8 weeks old if you plan on keeping him so he doesn't breed back to his mom or sister. As for grain bucks really shouldn't be getting any grain. I give my bucklings about a hand full of sweet feed up until they're 4-6 months old, Then i completely wean them off of grain and strictly stick to timothy/clover mixed hay diet (Unless i'm breeding them, then i'll give them a little bit of alfalfa pellets)
I'm assuming the mother is still nursing? If so she definitely needs the extra grain to keep up milk production since she's now in a new environment and still adjusting, which can reduce milk production. I buy a goat sweet feed mix and mix in some alfalfa pellets for my does in milk.
can you ask what their previous owner was feeding them? The amount of grain she was giving the doe sounds good. i'd look into what kind of feed she was giving her and try to see if you can get the same for them.
I provide minerals 24/7 for my goats. i use goat meat maker loose minerals for them, I don't use blocks. Goats can ruin their teeth by chewing on them so i always use loose minerals to be safe.