* "Us" is a bit informal. It sounds more natural to say "we" in this context, especially if the recipient is someone you're trying to be respectful or polite with.
* "Papa" is a bit informal. It depends on the context. If you're writing to a child, it's fine. If you're writing to someone more formal, it's better to use "Dad" or "Father."
Here are some better options:
* Lots of love from Dad and us. (More formal)
* Lots of love from Papa and we. (Less formal, but more natural)
* Lots of love from Dad and [your name(s)]. (More specific)
Ultimately, the best way to phrase it depends on your audience and the tone you're trying to convey.