Can your husband's children take his property after he dies?
Not unless they are legally entitled to it. Chances are that they are going to get some of it. If he died without a will, intestate, the standard distribution in most states would split the assets in half, one half each for the spouse and for the children from prior marriages.
If your husband is still living, he should clearly have a will drawn up that lays out his desires for the distribution.
In either case, you should consult a probate attorney for the state or province you live in.
A bit more:
In cases where one spouse owns property before marrying a second (or more) time, they can have a prenuptial agreement drawn up before getting married that will allow their surviving spouse usufruct (use of the property) for life. This means the surviving spouse will be allowed to live in the family home until their death or they remarry, depending on the wording of the prenuptial agreement and/or will. But the surviving spouse will not be able to rent or sell the property, or to leave it to anyone else. And after their death, it will then go to the children of the one who originally owned it.
There are also cases where the entire property is left to the surviving spouse, with the exception of forced heirship, where state law requires a certain amount or percentage to be left to the children of the deceased.
Either way, it is always a good idea to have a prenuptial agreement and/or a will, but especially a will. Never rely on the spouse or the grown children saying they would always "look out for the other" because greed or a sense of entitlement often results in people losing all sense of fairness and common sense.