Preheat oven to 375 degrees. Line a large rimmed baking sheet with parchment paper.
Bring phyllo pastry to room temperature.
In a large skillet, melt 1 tablespoon butter over medium heat. Stir in onion, pepper, celery, green onion, garlic or chives and shrimp. Cook, stirring occasionally, for 5 minutes or until shrimp is cooked and vegetables are soft.
Reduce heat to low and stir in the crabmeat, cream cheese and seafood seasoning. Cook, stirring constantly, until cheese is melted and incorporated. Season to taste with salt and pepper. Add a bit of lemon juice, if desired. Set aside.
In a small saucepan, melt remaining butter.
Place one sheet of phyllo on a large cutting board and brush with some of the melted butter. (Cover remaining phyllo with a damp cloth to prevent drying out.) Place a second phyllo sheet on top of the buttered one and brush with butter.
If using large phyllo sheets: fold in half lengthwise to form a 8- by 13-inch rectangle; brush with butter. If using smaller sheets: repeat 2 more times, for a total of 4 buttered sheets.
Mound 1/4 of filling in a strip at narrow side of phyllo rectangle, leaving a 1-inch border on the sides.
Fold over bottom edge of phyllo just to cover filling. Fold in edges on the long sides to cover filling and roll up.
Place, seam side down, on prepared baking sheet.
Repeat 3 more times to make a total of 4 bundles. Brush top and sides of each bundle with melted butter. Bake 30 to 35 minutes or until golden brown and heated through.