New kitten worries

Hi Alex,
I have an elderly cat (Louis). He is a bit grumpy and set in his ways. When I brought my kittens home, I had a sort of pop-up play pen for them (I bought it on Amazon). The kits did not spen a lot of time in it but it was very useful for times when I needed to know where they were for a minute of two ( doors open to bring in shopping etc). It was also perfect for introducing them to Louis. I kept his routines absolutely the same (he has always spent a lot of time outdoors) but he had to walk past the pen to get to his food in the kitchen. Louis would stop a sniff the kittens and they were very keen to meet him. He would growl too, but that lessened after a week of so. He would sometimes refuse his food first time too; so I just let him try again later. I would then let the kittens out while Louis was around (but not eating) and supervise very carefully. He was a bit cross and said some bad words (!) but these meetings were short and carefully managed. 3 or so months on, I would say Louis tolerates Dru (remaining kitten). He will let her follow him around (she is his fan girl- absolutely adores him). I think that winter will mellow him, as Dru is warm and snuggly. I expect to find them curled up together at some point.
Long story but I guess what I am trying to say is, put Pumpkin’s needs first (kitten needs to know who is boss). Introduce v slowly (a barrier between, that can be seen and sniffed through is good), keep contact short and be there to intervene and manage meeting, and it takes time (don’t get disheartened if kitties are not best pals straight away).
I hope all goes well:)