If I have old syringes left over from old fertility treatments are they safe to use?

No. Medical supplies should not be used after their expiration date. If there is no expiration date, a good rule of thumb is to not use beyond a year after purchase. Used needles and syringes should never be re-used.
If unopened. Most old medical supplies in their original package are safe for most uses. If they have been opened or used, then sterility is no longer guaranteed. For what use do you want them? Personal medical use? Then observe sterility. For hobby use with no risk of bodily penetration - no problem.