To answer your immediate question: “Is there anything wrong with this practice?,” the Torah addresses this very question in Numbers 9:6 ff., and establishes a holiday, Pesach Sheni, “Second Pesach” for those who could not celebrate at the appointed time. The Torah is explicit: Pesach Sheni was for those who were impure, and therefore could not offer the Pesach sacrifice, or for those who were travelling.
(Sorry. Travelling meant someone who was on an overland trip, by foot or by mule, to a distant country; or someone who was a multi-week boat trip. It doesn’t refer to someone who was on a voluntary cruise or was travelling by air.)
Then the Torah states (9:13): But if a man who is clean and not on a journey refrains from offering the Passover sacrifice, that person should be cut off from his kin, for he did not present the Lord’s offering at its set time…
My guess is that this question will get different responses from Reform and Conservative rabbis, and I am Conservative. From my perspective, the question is this: can we arrange Jewish life around our schedules, or must we arrange our lives around the Jewish calendar? This question, in turn, goes to the heart of religious practice.
I see Jewish observance as a discipline, a set of rules by which to live that, taken cumulatively, bring us to live a holy life – in modern terms, a sense of spirituality. As with other disciplines, the rules don’t always make sense and are often inconvenient. But unless they are offensive, they must be kept. When it comes to Jewish practice, there must be a surrender of one’s own will to God’s will in order to achieve that sense of holiness.
At the same time, we do live in 2010 when attitudes toward religious life have changed. So, here’s what I’d suggest: Have seder(s) on their appointed nights, even if small ones. And then to another one when family arrives. While it is surely more time in the kitchen, you can still maintain Jewish law and then have your family join you. You can see the first s’darim as preparations for the big one.