The plant in the top pic is in a pot too small for it, which won't help - the lower one won't last much longer in that pot either, though its not desperate. If a plant is potbound, its difficult for it to get enough water - the ratio of soil to roots is out of balance, so any water isn't held in the soil for the plants to access as and when they need to.
That said, the second one looks as if its either suffered drought or been exposed to strong winds/strong sun.

The presence of ants inside the pots isn't good - if they nest in there, they will chew through roots which are in their way when they want to enlarge the nest. Get a jeycloth, cut it in half and place it in the bottom of your pot, fill with compost and plant, and ensure that the pot is stood off the ground, either by the use of pot feet or with bits of broken roof slate or similar, to give a bit of clearance beneath. Dust the surface beneath periodically with ant powder.

Its been a bad year for Acers - mine have been fried by the sun, then wind damaged, then from lack of water then a deluge of water! So I have some crispy red Acer, a leafless dissectum, two healthy dissectum (after I pruned off the worst) and one red Acer (to replace one I put too much soil around and rotted the bark!)

Repot the first Acer. When did the leave fall off? It is not the best time to repot but your Acer is not going to lose leaves because of root damage when it has none.

The dissectum is still a nice shape. It will look glorious next spring.