Seeking advice about this is a good idea. Even though the blended or 'rearranged' family is a very common scenario throughout the western world, the fact that it is commonplace doesn't mean that it is a simple matter. Nor does it mean that it can't go very wrong - despite our best hopes and intentions.
In all the happiness of falling in love, it can often seem impossible to imagine that everyone won't share the happiness. But, as you know from your partner's children, this is not the case - and understanding how they feel can make a big difference to how ultimately your relationship with their mother will fare.
It sounds like it would be wise to wait a bit longer before moving in and to spend some time finding out, in discussion with your partner, more about how best to manage in this new environment - in other words to gather as much understanding and information as you can about how it feels for her children right now.
Always remember that this is less about you as a person and more about the predictability of child psychology and the impact of change. Adjustment, grief, and divided loyalties are often around in the aftermath of parental separation. If separated parents are in conflict then these features take longer to resolve and can be intensified by the arrival of a new partner.