Hi Welcome to the forum

,
'Sé an grá an oidhreacht is mó 'Love is the greatest legacy'*
*
mó (from
mór 'great'), has a range of nuances, many of which would fit the context here, making the statement quite ambiguous and open to interpretation. For instance, it could also read as 'love is the biggest/ largest legacy'.
Without loosing the sentiments of your original request, I would propose something similar to:
'Sé an grá an oidhreacht is buaine 'Love is the most enduring legacy'
Wait for more input. Cian
PS. in Irish font:
'Sé an grá an oiḋreaċt is buaine
_________________
Is Fearr súil romhainn ná ḋá ṡúil inár ndiaiḋ
(Amhlaoibh Ó Súilleabháin)
Please wait for corrections/ more input from other forum members before acting on advice
I'm familiar with Munster Irish/ Gaolainn na Mumhan (GM) and the Official Standard/an Caighdeán Oifigiúil (CO)