My brother took my father and had a will drawn up 2 months after my mother passed away. He has dementia, he doesn't know what he does day to day.

If your father was truly not competent to make a new Will at the time he made one, OR if your brother was unduly influencing your father at the time the new Will was made (even if your father was competent), then no, the Will may not be valid. Until your father actually passes away, however, if he is a Georgia resident you are limited in your ability to do anything about the Will now. If you have a copy of his prior Will (or the original of his prior Will), hang onto it. Also, you may want to try now to start gathering evidence of your father's condition and your brother's actions, in case your brother tries to offer the Will for probate after your father's death and you need to challenge its validity. On a more pressing note, however, if your brother has actually pressured your father into making a new Will, then there may well be other activity going on, and this other activity may be threatening your father's finances and, possibly, even his physical and emotional safety and health. In many cases, a child who has a parent make a new Will disinheriting other children does not simply wait until the parent dies; they take the money and other assets before the parent dies, often by getting a power of attorney or trusteeship of a trust in place and then abusing the powers granted to improperly benefit the child. A person who is trying to influence a parent may also try to cut the parent off from other family members and from friends, and, in some cases, may actually neglect the parent's physical health and well-being or actively abuse the parent physically or emotionally. If you believe any of these activities are going on, then you should strongly consider taking action to protect your father from your brother. This may require you to seek appointment of a guardian and conservator for your father, possibly in addition to taking other legal action. You should consult an experienced elder law attorney who works on contested guardianship and conservatorship matters as soon as possible. If nothing else, you can learn more about the kinds of things you should be looking for--red flags that can mean something very bad is happening. Please don't wait if you are really concerned; your father's life, health, and money could all be at serious risk.