We live in DC and the entire divorce, child support, child custody has been the same DC case. He is only going to be here that that particular weekend and presumably return back to his homeless living in NY. I take issue with him expecting that he can just get the kids this weekend on such short notice like we don't have plans or have went on with life for the past 2 1/2 years without him being present in any matter. I have no issue with scheduling a visitation this weekend, but not a sleep over especially when he no longer has a address in this area and will not provide me with the location.
The problem is:
!) You have a court order,
2) You did not change the court order to reflect the status quo, and
3) You have not indicated that there is any evidence that Dad is a danger to the children.
You have stated that Dad is bi-polar, but you have not indicated that he has violent spells, or that he has ever endangered the children. Therefore, you cannot say that you are withholding parenting time "for the safety of the children".
Additionally, at their age, the children know who Dad is. They don't need a "reintroduction" time. Do give them a phone to contact you (in an emergency), and do insist on knowing roughly where they will be staying.
If the kids have activities that are scheduled to occur in the time that Dad wishes to exercise parenting time, you could suggest that he take them. While he doesn't
have to, it might help for them to feel like it's a "normal" weekend, and help him as well. (Costs him nothing and gives him a mini-break. Gets to see them interact with their friends, etc.)