Well , to me it seems like he is suffering from Extrapyramidal side effects of quitiapine (seroquel) , but you did not mention the dose as you are not aware of it. Nevertheless, it is most likely that , the symptoms which you have mentioned suggest of extrapyramidal side effects.
The second possibility could be lithium toxicity, or difficulty in adjustment to lexapro.
So, i would sugest a few things you should do.
1) Go to the doctor who has started him on seroquel and ask him to carry out a thorough clinical examination and rule out Extrapyramidal side effect of seroql. If it is infact Extrapyramidal side effect then seroquel needs to be discontinued at once and a new anti psychotic will be started.
2) Carry out serum lithium test on your husband in a patho lab, and this will rule out any lithium toxicity.
3) Unless , these 2 possibilities are not ruled out , you may continue with lexapro.