Is it then permissible to divorce them?
Yes it is permissible to divorce, as Allah explained in the Quran. The husband can ponounce the divorce the wife, can ask, but if he refuses she has -theoretically- only two options which are usually need the wife to ask for at a court khula' (in this case she might forgo some or all her mahr to "buy herself free") and faskh (this is only possible in a few cases).
What the Muslim brother have bad deeds?
Talaq or divorce is called in a rather da'if hadith "the most detestable among the lawful acts", see for example sunan ibn Majah and abi Dawod.
Ibn 'Othaymeen said about it:
This hadeeth is not saheeh, but its meaning is sound: Allah hates divorce, but He does not forbid it to His slaves, so as to make things easier for them. If there is a legitimate shar’ee (religiously legislated) or regular reason for divorce, then it is permissible and depends on the likely outcome of keeping this woman as one's wife. If keeping her will lead to something that is contrary to sharee’ah (Islamic law) which cannot be avoided except by divorcing her, such as if the woman is lacking in religious commitment or chastity, and the husband cannot set her straight, then in this case we say that it is better to divorce. But if there is no shar’ee reason or ordinary reason, then it is better not to divorce, rather in that case divorce is makrooh (disliked). (quote from this fatwa)
So if you pronounce a talaq to your wife this doesn't make you a sinner, as talaq is a halal act. But this also means it isn't halal to marry somebody with the intention of talaq is this is a kind of Mut'ah which is haram among the sunni schools of fiqh.
Also talaq as described in the verse above means that your wife must stay with you until the end of her waiting period (which is more explicitly described here 65:1-3). Yes she can leave you but you are not allowed to force her and still must care and stay in charge for her during the time.
Also we are asked to be kind towards our wives no matter what
... And live with them in kindness. ...(4:19)
I recommend you to read other translation and take a look at tafsir.
But if they however separate (and this is allowed as shown) then Allah will enrich each of them from His abundance.
What if he was then to marry someone else?
This would mean if you intend to marry an other his former wife might get to know this and this may cause harm and may be a source for a sinful interaction between both of them.
But of course the husband is allowed to marry an other.
So this is why my recommendation would be: take your time to get to know your further wife don't hasten do istikhara, ask her to do istikhara too, try to find out commonalities and differences etc..
I myself due to the fact that my wife lived in a different country have been engaged for more than two years and I made istikhara many times again and again and every time we had a kind of dispute we spoke everything out, why one of us felt bad and what exactly made him/her feel so etc.
Finally I'd like to add a couple of ahadith:
This hadith indicating that one should take his time to choose a good wife!
This hadith indicating what makes out a good wife!
This hadith indicating that marriage, divorce and tacking a wife back is a very serious matter!
See also this fatwa on the rights of the spouses.