Rather than having seams between the tweed pieces (which may be difficult to flatten nicely) I would zig zag near the edge of each piece to stop it fraying - possibly using a contrasting colour. I think that would give a nicer finish than overlocking if the raw edge is to be on the right side. Then I would overlap the pieces and sew. Alternatively don't finish the edges in advance, instead overlap two pieces and then zig zag them together. This would join the pieces and finish the edges.I'm making a patchwork Harris tweed jacket and will be joining the pieces by overlapping them and zigzagging them together. (Pearl Red Moon Zambesi jacket). Many of my tweed pieces are quite small.I have put raw edged Harris tweed patches on a coat before now. The only finishing of the edges was the machine stiches I used to attach patch to coat. The odd thread has come off the Harris tweed but it hasn't frayed.