Assuming you both pass all stages of selection, including medical, simultaneously there's no reason why not, if there's enough places available for you to both start RT together, but it seldom turns out that way.
Not everyone starting Recruit Training realistically passes out with the same troop, so although it's possible, I wouldn't lay money on you starting the selection process & completing training together.
I dont think there's any "guaranteed" way of ensuring you would both be on the same PRMC mate let alone start RT together, theres to many variables to consider e.g passing pjft, eye tests, medicals, application forms arriving on different days!
Only thing you could do is ensure your ready for every stage of the application and pass everything first time.
hi, yes it could be possible if you are around the same standards of fitness and the rest, me and my mate are doing it and hopefully going through together but i did met a royal marines who did go with his mate and passed out in the same troop together and then got posted to the same unit so it could be possible, bus as long as you and your mate are at the same stage, and also i would have a word with the afco they will try there best to keep you two together aslong as there is no holdups.