ainehannah is correct in her translation but her spelling is slightly off.
In Irish (Irish Gaelic), Timothy is generally translated as Tadhg, the diminutive (or Timmy) is Taidhgín.
There is also a biblical translation which is Tiomóid, but it's really only reserved for the bible.
In Irish Gavin exists only as a surname, Ó Gábháin for men, and Uí Ghábháin or Ní Ghábháin for women.
Dylan has no Irish translation.
In Gaelic (Scottish Gaelic), Gavin is translated as Gabhan.
I'm unsure of the translations for Dylan and Timothy.