Without a bit more context the best 'do' I can give you is 'do restore the windows'. The best 'don't' is 'don't set fire to them'.
General thoughts:
First cut pitch pine is probably better than any timber you can buy today. Repair not replace where you can.
Where there's rot, splicing in a new bit is better than slathering on the woodfiller - but needs more skill to ensure a good fit.
Where there's rot, cut back to good wood. You know what good wood looks like. Repairs onto wood that looks wrong but feels "hard enough" generally fail quickly.
Think LEAD PAINT. Read up on it before stripping anything.
Wood doesn't rot because it gets wet. It rots because it stays wet. Modern high street paints tend to put a plastic film over the wood that cracks, lets water in, doesn't let it back out. I am a fan of linseed paints - others will disagree.
For sashes, paint everything you can see with the window shut. Don't paint anything else (but wax it if you wanna be a pro). Exception is around the lower areas of the inner stiles and staff beads.
If your building is listed ignore all of the above and agree your plans with your conaervation officer.
Thank you so much for replying! I am trying to load the photo , but technical hitch…just world like to know if a multitool drill type would damage . Can I use filler? Etc I will upload the photo as soon as iCloud lets me!
Thank you so much for replying! I am trying to load the photo , but technical hitch Wondering about the cordless rotary tool. It seems like hard work chipping off the old paint arounf the metal part of the frame.