I would suggest that the gift come from you and the children or just the children. I would keep the gift generic, maybe have the kids do a craft for her. Do not buy her anything personal. A gift card to her favorite store may be a good one.

I wouldn't offer up an invitation to join you and the kids on vacations this summer. It would be more appropriate to offer this up closer to the time of the vacations because anything can happen between now and then.

Keep the focus on Christmas and your kids for now. Involve them in the gift giving process.

Sit quietly, the answers will reveal themselves when you least expect them to.
The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.