I'm no expert, but I too am applying for my in laws to come from India, You can possibly apply at the same time, but you'll be risking it a bit i think. The Visa lasts for 6 months, so if he is staying for only 1/2 weeks then i may be fine, but will be at your own risk.
Taken from the goverment website regarding standard visit visas:
- You can apply for a visa up to 3 months before your date of travel to the UK.
- You should get a decision on your visa within 3 weeks.
- Check the guide processing times to find out how long getting a visa might take in the country you’re applying from.
- You can usually stay in the UK for up to 6 months.
You might be able to stay for longer if:
- you apply (and pay an extra fee) for a long-term visit visa and you can prove you need to visit the UK regularly over a longer period
- you’re coming to the UK for private medical treatment - up to 11 months
Hope this helps you