Hire a good workshop to repair your bikes and make sure they follow correct repair procedures even involving proper sealants, you should buy a case of spray chain lubricant and have someone/riders spray it on the chain every 2 weeks for proper service life. Similarly a small supply of WD40 and some proper degreaser and shampoo will keep the bikes like new.
For oils buy an old 20 litre oil bottle/drum - and get it filled at a proper licensed depot with the oil brand of your choice bearing oil quality marking of API SG 20W50, caltex, Total, Shell all sell it. It will be considerably cheaper than buying small bottles.
You can even get wholesale prices for disposable spares if you are constantly maintaining them e.g. air filter, gasket sets, clutch friction set, chain case, brake shoes, buffers, bulbs, lens covers. But it all depends on how you have your system setup, If its all dependant on mechanic ustaad then there is a pretty high chance that your parts will get nicked.