Nice looking boards
I would NOT fill the holes with epoxy. I would use wood pegs or dowels instead. You can make them yourself on a drill press since they are not all that long. Use a file as the spin around on a wood screw or bannister bolt, then saw them to the correct length. You can also use a table saw... see you Tube for how to.
As far as the lead, they don't look painted, just sealed, but I could be wrong. If they are really old, then they may not have any lead, just a wash of some sort.
Leg design ..... use mortices and tenons and you can't go wrong. A through tenon that's wedged would be appropriate.
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)